I've thought about whether it was just something that spooked him, and I think that could be part of it, but it is not specific to going a different direction out the door. He refuses to make any detour off of the walking path along the ocean, even if it's to another area of the park, no matter how far away from the house.
He has always had a strong attachment to that route; he gets to run off leash and has bushes and beach to explore, so it's definitely the most exciting place to walk in the neighbourhood. I wonder if maybe I've had him long enough now that he's feeling comfortable enough in our relationship to try to start testing me, and see what he can get away with? (When I got him he was VERY submissive, and he's built up a lot of confidence over the months.)
Or,possible that he's still not yet feeling 100% better from his infection, and that he wants to walk in a place that makes him feel safe and secure (i.e. bushes and beach)?