And for Rand, that's reasonable - while he didn't have all the information either, he had no way of obtaining it with Egwene telling him nothing. Mat, on the other hand, has reports from Vanin that tell him there are hundreds of Aes Sedai, and has seen the crowds for himself. He has that information. I doubt it influenced his perspective on Salidar, or else he wouldn't be a very good general.



That he's making incorrect assumptions?

I was going to say that I could understand if he holds the common wetlander belief that Aiel are violent (which is still less forgivable in his case, since he's spent months with them), but then I re-read the scenes. He jumped to this conclusion BEFORE she even took out the knife! So all he had to go on was that Aviendha and Elayne like Rand, and that Aviendha wants to speak to Elayne. And the first thing he thinks is that he hopes there's no trouble there. Never mind that they have mutual friends, or that Aiel of all people are used to sharing a man (though I can't remember whether he'd know this by now - it's not as if it's a secret, and we've all seen examples of it...). There are plenty of ways in which he could have taken that, including completely neutral ones (e.g. Aviendha has a message from Egwene to Elayne), and there's no evidence that he really even considered the possibilities.

And as the cherry on top, he still thinks Aviendha wants to kill Elayne on their way to Ebou Dar. Days after they've met. After they've shared camp. Even when she refers to Elayne as her "near-sister" and is angry at Mat for disrepecting her, he doesn't think that his conclusion was wrong - he thinks that this is some women-hating-men thing! Hence my comments on Mat never realising he's wrong. He has plenty of evidence showing that Aviendha does not want to kill Elayne, and somehow still manages to believe otherwise. Incredible.