So far in the series, characters who invoke the Light or swear by it in their own thoughts aren't DF. So far, Jordan has stuck to that unwritten rule of fairness to the reader. He's done the deceptive POV only with Verin, and it was misleading only inasmuch that Verin had joined the Shadow without giving it her true allegiance, thus she had no reason not to think like someone belonging in the Light in her private thoughts.

The fact Thom exclaims in his thoughts once "Oh Light, Owyn!", in the moment Moiraine used his guilt over this to manipulate him aside, in the same POV there are plenty of genuine information about Thom's "hidden reasons" to help the boys and especially Rand, and it all has to do with a perceived debt to Owyn he's trying to repay through Rand. There's also the situation that Thom expressed the desire to retire and go away, but he just can't bring himself to. Not the motivations of a DF and in complete contradiction with the idea that Thom has been placed near the boys.

I think you're grasping at straws with Thom, really:

This is very strange, why would Thom know Fain?

Because both of them travel around for a living and hang around village inns, both of them are newsmongers and information gatherers beside their real job, and they are both active in the same areas so their paths have crossed often. Often enough for Thom to have noticed Fain revels most in spreading the bad news around.


Second, Thom isn’t afraid of the Fade at Whitebridge like a normal person should be

You mean Thom is more courageous than average. That's no surprise, he's proven a very daring man, especially when those he's decided to protect are in danger. Why he decided to face the Fade was a matter of self-sacrifice, and the motive for it is explained in Caemlyn: it's all about his guilt over Owyn. Thom perceives this as a taint on his soul he seeks to atone. To an extent, it seems he once saw helping the boys as some sort of punishement the Pattern threw at him. Those feelings are exacerbated by the pull of ta'veren, making it quite difficult for Thom to abandon the main cast, even though he's wanted to at some point.

Thom, above all but Moraine and Lan, should know the stories of Shadar Logoth and its dangers.

That's irrelevant. First, you exagerate the role Thom should have played - there's a lot of things he doesn't know or about which he knows the "official version" and not the more obscure knowledge the WT has about something, and then if he were a DF he would have had all the more reasons to freak out for the boys in SL, which has a dire reputation among the Shadow...

The boys had already been forwarned strongly, and Thom didn't really know what they were up to. Simply enough, Thom overestimated the boys's common sense, just like Moiraine and Lan did...

Fifth, we know nothing of Thom before he was a court bard.

That's not really true. We do know some things, and we can deduce others. It's not because it's never been confirmed Thom is Andoran (even though it's fairly obvious from his looks, his deeper of Andor etc.... and Andoran political players would not easily welcome and trust a foreigner in the role of grey eminence Thom has played with the Trakands) that his past is so mysterious.... Before becoming Morgase's court bard a few years before the Aiel War, Thom had been House Bard to her mother, Maigdin Trakand. Then we know it takes many years to train as a gleeman, and even more to attain the Bard status, which tells us pretty much what has been Thom's main activity before he was hired by House Trakand: apprentice to a Bard.

It's fairly obvious the motive behind the pseudo mystery of Thom's exact past, nationality etc. is that Thom is supposed to remain perceived as a character from nowhere and everywhere. A bit the same way Noal's nationality wasn't fully confirmed until TOM, though much like it's easy to deduce Thom is almost certainly Andoran (he's no Borderman, don't fit at all the physical profile of a Cairhienin and shares the opinion of the average Andoran about them (same about his opinion of Murandians_ and as he's not Tairen and clearly not from the South... and all his ties are in Andor and it's a nation he doesn't speak of as foreign... it piles up), the clues were always there that Jain was Malkieri.

Sixth, Thom knows a lot about the DO and shadowspawn.

He knows what you'd expect a well-travelled gleeman to know. His knowledge is similar to Loial, even less scholarly. The Shadow and shadowspawn must be in tons of his stories. Thom's knowledge on the Shadow fell short on a couple of occasions. He's no expert on the Shadow.

Seventh, Thom and Rand have not seen each other since well before Rand’s epiphany and Rand gaining his "Darkfriend vision ability".

So do tons of other characters... all of Perrin's group, most of Mat's... why should Thom be singled out for that?