The guy's switched to a party more in line with his own positions, and the move is likely to benefit him politically.
I'd say that's not so much "OK, which is it?" as "hey, the system sometimes works".
That's how a robust human system works - playing it straight is usually advantageous.
OK, there are side details that amplify the effect in this case. But for the most part, belonging to the party you agree with most should be good political move.