I agree, it does appear that he's capable of incredible stupidity (presumption of innocence aside).
The resisting arrest charge may be based on nothing more than he went into someone's apartment to evade the officers who were pursuing him. Or he may have physically resisted the officer who was arresting him. For example, if he were ordered at gunpoint to drop to the ground and he didn't immediately comply, that could be seen by the officers as resisting arrest. Or he could have actually scuffled with one or more officers. But if it were the first one (ducking into someone's apt to evade the officers), I can imagine them dropping that charge if he agreed to plead guilty to the misdemeanor possession charge.
Yes, the NBA could choose to make a big deal out of this (above and beyond the actual crime charges) and punish Randolph to the fullest extent possible. But that just doesn't seem likely in today's world.