What's odd about playing a two-pair/set/QJ
this way?

Pretty typical set line with 4 to the flop on a very draw-heavy board...

For weaker or ... weakest? I tend to fold the flop on this type of TPTK hand - I'm not likely to improve in any way that helps me to continue to bet out, and the pot is now bloated.
Sometimes I will call here and check-fold the turn...I am mostly going for a reasonably priced showndown - it helps a lot if another diamond shows up and forces him to slow down.
Certainly there are times I will felt this hand - but that would require a read.

I like to just bet-bet-bet and be smooth-called down by weaker pairs when I have TPTK...it doesn't happen often enough really