I assume it has to do with sneaking the machine in and out of a place. The other alternative is something to do with storage. Maybe it's a backup machine they want hidden somewhere in case the feds seize all his electronics.

That last one makes the most sense, and explains why he didn't divulge it. That way, when the author is raided, they aren't going to ask, "hey, where's that computer that, comes in the smallest box?"

I'm imagining the author has this big book case, and one of the books is hallowed out and has an Apple machine in it. Maybe it's built into a false floor of a cabinet.