Getting donk bet by a TAG

[Absolution]

This guy is an overly tight TAG (20/12/2 type.) I don't have much on him besides his stats. He limped a mid pp UTG earlier and then donk bet a set on the flop after being raised pre-flop.

PokerStars 1/2 Hold'em (6 handed) Poker Stars Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

Preflop: Hero is Button with J[img]/images/graemlins/heart.gif[/img], A[img]/images/graemlins/spade.gif[/img].
UTG calls, <font color="#666666">2 folds</font>, <font color="#CC3333">Hero raises</font>, SB calls, BB calls, UTG calls.

Flop: (8 SB) 5[img]/images/graemlins/spade.gif[/img], 4[img]/images/graemlins/diamond.gif[/img], 6[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, <font color="#CC3333">BB bets</font>, UTG folds, Hero calls, SB folds.

Turn: (5 BB) 9[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">BB bets</font>, Hero calls.

River: (7 BB) 7[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">BB bets</font>, Hero folds.

Final Pot: 7 BB

What do you think a flop donk means from a guy like this? I called the turn because I expected him to give up on the river quite a bit and I thought my outs were likely good if he had a small pair, for example.