Only he and perhaps a few close family members can know if he actually is, but his claimed religion is Russian Orthodox. I don't really see much reason to doubt it.
His is a former KGB officer, an organization hardly known for religious tolerance. Most Russians claim Orthodoxy, including me, but Putin is the last person I would associate with any sort of piety.
I'm aware of those things, and obviously he knows that everyone else knows that too. If he says he is religious, I don't think mere conjecture is enough to assume that he isn't.
The actual reality of what he thinks can be known only to himself, the best we can go on (for him, and indeed anybody else. Hell, even the pope...) is what he claims.
