[Freudian]

As always with blind vs blind play there is a guessing game and I think you can't interpret bets as you normally would (for example when it comes to protecting your hand).

But if you look at it from villains perspective, couldn't his play be interpreted as trying to build a decent enough pot to at least get paid off by the river, against what he must think is a poor hand most of the time. At least I would assume there is a very big chance of a fold if I bet big on the turn (since heros flop bet look like a standard "please let me win this hand" bet) and a very big chance of a check if I check the turn. Thus a small bet makes sense in sweetening the pot.

Alternatively he has something like JT and is a bit unsure of the strength of his hand and the meek turn play by our hero convinces him that his TPGK is good and he tries to get paid on the river.

For all I know villain could be a donk with A3, thinking he is good all the way. These kinds of hands at the lower limit are among the hardest to analyze in any meaningful fashion. I have had people limp/postflopown me with KK where no bet until the river makes sense on any scale known to humanity.