Seems pretty positive to me.
Everyone's entitled to change their mind. Burton could have initially liked the movie but changed on reflection.
Also Burton is an actor and he could have been playing for his audience. It probably never hurts to say positive things about Gene at a Star Trek convention. And if the audience were chiefly 24th century Star Trek fans then maybe he thought he would share his movie misgivings with them.
Everyone is entitled to change their mind, and I think remaining open to opportunities to change one's mind can only be a good thing. At any rate, the negative remarks about J.J. which were attributed to Burton came before the movie's opening here, and I'm not sure it was ever confirmed that he'd actually said that in so many words. Anyway, I'm willing to give him the benefit of the doubt, since to my knowledge he's been pretty fair in the past.