50nl
UTG opens $1.5
MP folds
CO 3bets $5.25
BU folds
SB folds
BB (hero) 4bets to $16.75 (KK) (100bb)
UTG folds
CO calls

pot $33.5 flop As 6d 4h
hero bets $8.5
Villian shoves all in
Hero $25 to call

Is this an easy fold ? Fish is unknown preflop but believed to be highly likely to be fish due to unknown screenname and not seen on other tables. On flop , I believe villian could be 95% fish due to flop jam (dont see regs raising allin ). And identifiying what kind of fish it was likely to be, i found a bit hard, because its hard to quantify exactly what type of fish there are due to no HUD. But something like 50% loose passive fish, 33% sometimes spewy fish, and 17% whale.

I called thinking i had 25% , but now wondering if my decision had a bias. I've seen fish turn hands like 99-QQ into a bluff in these types of cold 4 bets pots . Maybe with the rational that most people don't 4bet AK and only have a lot of AA KK QQ in their range.

I figured the fishes pre flop calling range looks like JJ-99 (maybe not too many 99), a good amount of AQ and AK (a few less combos due to some 5 bet jams ), and some randomness.

So with AK and AQ being main value hands (about 18 combos) and maybe some random AX , Villian just needs to do this with 5-6 combos of worse dominated hands to have 25% equity.

Is this type of play rare? I feel like i've seen this spot somewhat frequently, considering that cold 4 bet pots are rare.