I was listening to the radio quite a bit yesterday evening while driving, heard excerpts. I would say that most of his answers were politically correct, he was saying the right things. It is hard to read too much into things, but he definitely became disgruntled at some point. He is not happy with the Celtics organization, but said all the right things about Boston and Boston fans.
The bit about throwing his phone when he heard about the trade seems a bit weird, he knew he was getting traded, it was just a question of when and to where. In fact, by that point, he probably wanted to be traded. So I am not sure I buy that part. As to Tatum, he was definitely pretty cool towards him. Said the obligatory "nothing but respect", but not much more. I expect there will be a big hug on the court at the first game, very respectful of course.
There are hints it seems that Tatum and maybe other players may have gotten a little tired of Brown's act, that is pretty speculative, but it is possible. Certainly the Celtics organization seems to have gotten tired of Brown's act (they did trade him after all). I am not sure how much of this has anything to do with any of it, I have my doubts that this was much of a factor if at all.