My justification for the super heavy all-in was cause he had a sizable stack and people at this blind call just to see what the other person has to make such a huge raise.
How weak a hand can he call with just to keep you honest though? The best flush draw he can have that you beat is Tx.

By raising in this spot against most players you make them fold out all their marginal crap and they will call you with hands that beat you. I reckon there might be an argument for his line being indicative of a flopped set... he bets small because he wants to try to fill up but doesn't want you blowing him off the pot (but i'm not so sure i like c/c'ing with a set on this flop). In which case he gets there on the river.

I think I bet the flop for a bit more: he's not calling here because you bet 3 or 4 cents less, he's calling because he's a fish and you are expected to bet in this spot with the vast majority of your range. I probably check/call down thereafter.

then again some bad players at 2NL will call that with the 8d.
The all-in raise is still pretty extreme. If he likes seeing showdowns, he's probably gonna pay a few more cents to do so (min-raise) but a whole dollar might make him actually think about things for a second (a second longer than he would to a min-raise).

I'm also thinking, were I bluffing in this spot with air, i'd be shoving in the hope he puts me on Ax and folds some weak diamond draw. But you definitely don't want him to do that here.

I think if he had the Ad he would have reraised you on the turn
Villain lead the turn and hero called.