Unless I'm totally off base, it seems like there are lots of hands villain could have that we beat.
1. No preflop raises mean catching just a piece of the flop may be encouraging, and ranges at that point are wide. Lots of draws.
2. The $30 bet into a $72 pot could be read as weakness, depending on stats. Villain could think his straight, set, or even 2 pr. is good.