He certainly can have a lot of other things here. The question is, how often do you think he plays his sets and straights this way? How many flush draws is he shoving here?

Results from http:\\www.HoldEmRanger.com
64 evaluations, 64 hole card combos

Board: 3s 2c 5s Th Js

Wins Ties Equity
38.65% 0.00% 38.65% ( 7s6s )
61.35% 0.00% 61.35% ( 33(33),55(33),A4(33),46(33),J5(33),As2s+,Ks2s+,Qs2 s+,Ts2s+ )

Close...but its still a fold if theres a 1/3 chance he is slow playing and can show up with J5 sometimes. More flushes hurt us, more slow playing and stupidity helps us. So perhaps its pretty marginal with no real read.

The real thing is raising button limpers PF, not 3 betting the flop, or betting the river stronger all make this a much easier spot.