Did he have his “brain freeze” because he is dumb? No, but rather because was speaking from prepared comments about which he has no real conviction or has likely given much thought. It is easy to forget vapid talking points (and he has demonstrated on multiple occasions) but one typically does not forget issues about which one has spent a great deal of time pondering.
Beyond the clear attempt at making up positions as he goes, consider Perry’s career in Texas politics. When it was expedient (if not required) to be a Democrat in Texas politics, Perry was a Democrat. Once it was clearly the case that being a Republican was more advantageous, he became a Republican. Then, after an election that seemed to indicate he was in serious trouble, he hung in there and found his way, at least rhetorically, into the Tea Party camp. It is not unreasonable to argue that most, if not all, of these moves were about finding the best path to career advancement as opposed to being about principles.