I'll agree that this finch is not typical of a House finch but I believe that it is one nonetheless. The male Cassini's has a rather bright unmarked flank and belly that strikes one as very clean and scrubbed. Your finch still shows notable streaking. The facial pattern is not screaming Cassini's and it might be a House finch that isn't quite well, which might cause the atypical behaviour and antisocial demeanour for a species that is often quite social. Animals also show odd behaviour near the end of their life, keeping to themselves and showing little fear of people. A dying rabbit once nestled down beside me. When I moved away a bit it closed the distance and nestled against my leg again. If I had a bottle of wine I would gladly have shared it. I offered the rabbit some of lettuce from a sandwich ... no interest. I told it a few stories but they weren't good stories because great stories never started with a salad ... wine would have been better.