he raised to 4 then bet 3 on the flop into a $16+ pot. Everyone is now getting over 5-1 to chase against your two pair--this is a major mistake. (despite the fact it is going to be hard for anyone to catch anything that'll beat that hand)

Betting 3 on the turn (into a $25+ is another major mistake--they can now chase almost everything and be getting odds to suckout on you)

Moving allin on the river with the cards that are out there isn't that bad. But he's really hoping somebody has also hit two pair when he might have been allin on the turn against someone else drawing dead anyway. Waiting till the river makes it more likely for an opponent with a weaker holding to fold.

Trips usually is a bit too anxious to get that stack in much earlier in the hand. He got a call--so your buddy should have won this hand.

He also should have bet more at least on the turn though.

I don't like the wait till the river strategy since it's way too easy for a weird board to hit and then the other guy won't call.

I wouldn't be at all surprised if you said the other guy had 35 though... lol