I don't know what the best answer is, but I do like to share my thought process and see if it helps (and to see what I can learn):
Villain seems a bit loose/passive for 6-max. I'm curious about his donk bet percentage and how "poker smart" you've felt he is based on hands of his that you've seen and general play at the table. That info should help you decide how to interpret his donk bet. Also looking at his turn aggression stat could help.
I agree that if he has some poker savvy and had a monster, he would either check and let you, the preflop aggressor, take action and then he could raise you or float. But we don't know that for sure and this is micro-stakes
I like reraising the flop. I would do that because I estimate that I'm way ahead on this flop. So I want to get money in when I'm good. I know there are strategies for Way Ahead/Way Behind (but not sure what they are!). He could be testing the waters with a hand like PP lower than QQ (other than 33) or AJ-AK.
The speed of his betting the turn is another thing I think about. Some say that a fast bet means he isn't thinking about what he's doing (or had already decided to bet before the turn). If he hit a monster, wouldn't he think a bit about how to get more money out of you? But I've also seen eager betters just auto-click 2/3 pot or pot.
I agree that in this case I'd fold the turn. I'd figure I'm beat with that A. I would like to hear from anyone about thoughts against folding (if anyone thinks that).
The micro FR cash thread
has had some discussion about donk betting and understanding what it means. Look starting at post #486 for some posts about it.