I suppose that in doing it in the form of a parable (or this parable, anyway,) I erred on the side of being memorable over clear, but that was what I had in mind when I wrote it. A dragon in one's garage is something where it's intuitively obvious that you don't want to go near, once you internalize the fact that it's really there. That's the kind of mistake that we've had millions of years of evolution to prepare us against making. Opening up the garage door to investigate is the sort of behavior that only makes sense when you haven't internalized the idea that there's really something in there that's liable to eat you.

Realistically, the man would probably be terrified if he had seen it eat other animals already, but I threw that in to make the parable flow better. The invisibility and inaudibility probably wouldn't be sufficient in real life given that, but they're stand in qualities for the sort of remove that might prevent one from internalizing a belief.