I guess you didn't bother to count the size of the pot.

After Terri's raise on the turn, there is 8.25BB in the pot. If BK just calls, she gets infinite odds on a 5-outer. If he 3-bets, she is getting 10.25:1 (plus implied odds) on an 8:1 shot. Her fold to his 3-bet is incorrect and loses money for her and wins money for BK. So his 3-bet turns out to be a great play.

-v