I agree that he should of pushed on the flop when he was 60% favorite. The reason he might call a shove on the turn when hes now a 70% underdog and has surrendered all fold
equity may be down to the pot
odds and whether or not he was committed.
If the pots offering him 2-1 there then hes gettin paid to call off all his chips with around 33% equity which he has (roughly) on the turn. If you can give stack sizes, pot sizes and blinds it would be helpful.
If he had already put in a decent amount of his stack and folding will knock him down to a point where its push or fold after that, then the moves makes even more sense.
Iv'e C bet before in position heads up, got raised by a weak ace (ace on flop, i'm the aggressor PF) and noticed i'd put myself in a position where id got a lot of my stack involved with an up and down straight draw. My chance of coming back after folding was marginal as the blinds would eat me up so i shoved for what fold equity I had. Got called by the marginal ace (happy it weren't a set) and drew out on it then got called a lot of names.
There weren't a lot you could do in this hand anyway dude cause 90% of the time the chips are going in anyway (and they should be going in on the flop IMO)!!
This is why monster draws are hard to get away from even when you play them wrong on the flop.