Anyone who actually believes 2 opponents who claim to hate each other in their pressers has to be at least a little bit dumb in my opinion.
Even if the fighters work themselves up to believe they truly hate their opponent, it's all just tactics, and it's so obvious because you see it instantly washed aside once the fight is over and they have the utmost respect for each other. Nick is no different.
The only fighters in my memory who have continued a beef even after the bell are Michael Bisping and (ironically to this thread) Nick Diaz - in some of his later fights at least... ... and most people HATED them for it... so I guess people are aware even subconsciously that it's all just hype-fermenting dramatics.