$11 - Please help me understand donkbetting

[Messy Harry]

This hand takes place early on, so I have no read on villain. After he donk bets the flop, he then leads the turn for a smaller bet?! So I raise him on the turn, he calls....and then again donk bets the river for a silly small amount? Is villain's play of this hand stupid? Advanced? If he's got a good hand, he's certainly not getting value out of it on the river.

PokerStars No-Limit Hold'em Tourney, Big Blind is t20 (9 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

BB (t1280)
UTG (t1490)
UTG+1 (t1590)
MP1 (t1520)
MP2 (t1520)
MP3 (t1450)
CO (t1470)
Hero (t1500)
SB (t1680)

Preflop: Hero is Button with J[img]/images/graemlins/club.gif[/img], A[img]/images/graemlins/spade.gif[/img].
<font color="#666666">2 folds</font>, MP1 calls t20, MP2 calls t20, <font color="#666666">2 folds</font>, <font color="#CC3333">Hero raises to t100</font>, <font color="#666666">2 folds</font>, MP1 folds, MP2 calls t80.

Flop: (t250) A[img]/images/graemlins/diamond.gif[/img], 6[img]/images/graemlins/heart.gif[/img], 4[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">MP2 bets t60</font>, Hero calls t60.

Turn: (t370) 8[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">MP2 bets t40</font>, <font color="#CC3333">Hero raises to t120</font>, MP2 calls t80.

River: (t610) 9[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">MP2 bets t40</font>, Hero calls t40.

Final Pot: t690

[Hercules]

First of all you shouldn`t raise AJ PF in this spot.
The thing with the donk...
In my experience the donklead is 85% nothing/midpair or a draw and 15% a monster.
His little bets are just so called blocking bets. And yes, his play is silly, but only if you punish him. If you just call his limit holdem bets, then he`s doing a good job in seeing a cheap shodwon.
In a 11$ i would go all the way with this hand on this flop. Raise him big on the flop and get it in on the turn. If he has a set, so it be. More often then not they call you with a weaker ace or weaker pair.