As played, it's probably a begrudging call.
Let's look at it from the button's perspective. They called the initial flop bet. On this board, that's likely a draw, or a monster. But what monsters are there? A set? A straight? With the flush draw, those both seem like hands to be protected. Especially with 2 other players. (You didn't include any reads, so I'm going with not completely clueless).
So I would tend to weight draws a bit more heavily. Then, seeing your raise, they may have viewed it as a good time for a semi-bluff, especially if they had the nut flush draw. They had about the right stack size to fold any 1-pair hand, and certainly any draws that may currently be ahead (pair + gutshot, pair + OESD). With a board that scary, they may even be able to fold 2 pair hands.
And even if they can't get them to fold, they've got outs to the nuts. (Their 9 outs would make a call at 2:1 correct, so why not push and get some fold equity).
All in all, I hate the C/R line here. Betting wouldn't be bad. At that point a big raise gives you info. And I wouldn't hate calling either, and seeing what the turn brings. At that point, a big bluff from a flush draw is a crazy move, not a decent move.
I think NLHTAP has a section on semi bluffing with draws, and when it's correct. I think that your raise made it correct here.