I wasn't thinking of burglary as a problem in need of the backup, but instead, your data getting into the hands of a stranger. You're basically doubling your risk of that happening, assuming your link is secure, and your neighbor is solidly honest and has a secure PC.
Instead, you could drop your encrypted disk in a safety deposit box and have physical security, encrypted data-at-rest and no network exposure during the backup process, no need to wonder how secure your neighbor's network/PC is.
Here in Atlanta, we had a 500-year flood at the same time California was experiencing massive wildfires.
Mudslides, earthquakes, floods, tsunamis, neighborhood-flattening gas leaks, the SWAT team trying to take out James DiMaggio/MOVE/David Koresh, or even the dipshit down the street burning leaves in a drought could take out both your houses.
The likelihood is small, but the consequences of failure are large. These are black swans. They don't usually happen...but they don't never happen either.
Y'know what's another huge risk, probably way more likely? Your backup failing. I remember being part of an IT project where an ancient SCA data drive went down on a database server. They had to get a replacement for the legacy hardware from the manufacturer's parts inventory, and spent 36 hours rebuilding the drive from backup tapes before figuring out that the database data itself had never been part of the server backup, because you'd have to disconnect the database to do that.