We'll have to wait for the OP to chime in on what exactly the property had issue with... but the only thing I can think of is they have a rule on no open-toed shoes/sandals/flip-flops for men, and considered Crocs to be in that category?
I've definitely heard that some properties in BKK are strict about the no open-toed shoes rule for both men and women, though that supposedly goes more toward cultural norms about exposed feet there.