That's right.
Honestly, I see no reason why anyone would hide their gambling habit from their partner, except of course they do not really value that relationship that much. There's absolutely nothing wrong with being a gambler and it shouldn't have to be to choose between gambling and your relationship, even if you're an addict, it's still important to let your partner know about your gambling habit because that can actually help you regulate or get over the addiction quicker since you won't have to always hide whenever you're doing it.
I can think of a valid reason, which doesn't excuse hiding it though, but it's maybe because gambling is viewed as something negative. Due to addiction issues, people always think of addicts when the topic of gambling is being discussed, thus, the husband knowing his spouse's views, preferred to hide it rather than be honest about it, because he was worrying about her reaction. However, the truth always comes to light, and he should have expected that one day, she might find out; he should have been open about it in the first place and discussed it before.