Why would they care what he does in his free time unless they didn't expect it to be His Time? That's the real question here.

And if they're going to have that sort of expectation - that it not be his time - then not being upfront about it is dishonest; an attempt to get someone in and then take advantage of them. No wonder they didn't get a good cultural fit if they were so dishonest that the poor guy's just figuring out how to deal with it now.