Think villain should bet bigger on the river personally after I call turn, our set is pretty transparent by the river so it's a fold for me. I beat nothing except a bluff and with 4 diamonds on board at this level I can count the bluffs on one finger; 222 would tank/check a lot of the time and so would Qx nearly always so the only one I can come up with is 9T with a diamond that would bet this small and that's pushing it.
Notice how our friend takes over the betting lead even after being raised, that's real scary and I need to tread mega careful. They do this to stop me getting a free river so maybe I can even fold out right there, but that's tough to do with a card to come!
If villain will stack off on a paired board I would call (and some fishy types will) but otherwise I can find a fold on the turn - sometimes.
A small value bet like this is often Jdx worried about getting raised, or a weaker flush like 89/9T with a diamond or something similar; Kdx and Adx go want broke obviously.
That's how I see it anyway but I am open to being corrected!
Just got up so hope I didn't just type waffle. Brain no work beer without.