Where are your parents?

The cat sounds to me like an abandoned cat who is going feral, rather than a born in the wild true feral. This makes things a little less frightening since it makes it more likely that the cat will come out at night when it's quiet and he's tempted by food. You are right in thinking that he could have tried the vent, got out and found another secure place. Please keep us posted since I know a lot of people on this forum are going to worry for the cat until we hear he is out and okay.