Yes it's that, but remember that Sitters humiliated Siuan in the Hall by associating her to her former Ajah, as if she still was a Blue. They tried to prevent the Blue Ajah from having representatives because with Siuan and Leane they already had.

About the friendship of Moiraine and Siuan I discussed this elsewhere. The only ones in the Tower who think this friendship forgotten are Siuan and Moiraine themselves. It's been referred to a few times by other sisters, always with the mention Siuan and Moiraine seemed to have distanced themselves on purpose.

They never confronted them about it until Verin did (or since) as Aes Sedai affect to stay out of each other's business and if Siuan and Moiraine wanted to pretend they never were close friends it was their business, but it seems few sisters who've known them have forgotten their friendship, or haven't puzzled out it's because Siuan and Moiraine wanted others to forget this they affected to be distant now.

Cadsuane and Seaine are some of those who mentionned them, and of course Elaida.

In other words, Siuan's and Moiraine's little scheme to hide they were close = big fail. The obtained exactly the opposite effect, everybody thought they affected otherwise because they were scheming.

And keeping this in mind, the whole confrontation about Moiraine in the Hall, insulting Siuan by implying she was still serving her ex-Ajah etc. was all quite relevant. It was all a "what the heck are you up to with Moiraine?" attack.