Hand that really confused me...

I'm a new poster here but longtime reader. I've been playing everything from 2/4-5/10 and i came across a hand on ps that really confused me today.
UTG seems a little on the tight side, and i haven't really seen him get out of line... button on the other hand is pretty fishy and i think i could stack him if he has top pair or better. UTG's cold-call of my reraise really confused me and in retrospect i probably should have either thrown out of a blocking bet or called river getting 2.5-1. What could UTG possibly have?

PokerStars No-Limit Hold'em, $10 BB (9 handed) pokerhand.org hand converter

SB ($970)
Hero ($1135.25)
UTG ($1521.75)
UTG+1 ($390)
MP1 ($530.25)
MP2 ($772.50)
MP3 ($1028.75)
CO ($1079)
Button ($583)

Preflop: Hero is BB with T[img]/images/graemlins/diamond.gif[/img], 5[img]/images/graemlins/heart.gif[/img].
UTG calls $10, <font color="#666666">1 fold</font>, MP1 calls $10, <font color="#666666">3 folds</font>, Button calls $10, <font color="#666666">1 fold</font>, Hero checks.

Flop: ($45) T[img]/images/graemlins/club.gif[/img], 5[img]/images/graemlins/diamond.gif[/img], 3[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
Hero checks, UTG checks, MP1 checks, <font color="#CC3333">Button bets $30</font>, <font color="#CC3333">Hero raises to $100</font>, UTG calls $100, MP1 folds, Button calls $70.

Turn: ($345) 7[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">Hero bets $225</font>, UTG calls $225, Button folds.

River: ($795) A[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">UTG bets $500</font>, Hero folds.

Final Pot: $1295