Hmm. You must pay attention.
It seems that the default storage (automatic) configuration doesn’t create a separate partition/volume for home (that in reality it has to be /var/home, in fact /home will be a symlink to /var/home).
So, if you used automatic partitioning during the first installation, when you reinstall Silverblue, it will reformat the / volume, wiping your home content as well.
Did you have a look to the documentation? Installing Fedora Silverblue :: Fedora Docs
The approach of reinstalling Silverblue is a bit contrary to the point of ostree. As long as it boots, you can restore the image to what it was after you installed it by issuing rpm-ostree reset. It’s even a little “better” than a re installation in that it’ll retain the latest overlay (patches) as well as keeping all the volatile information intact.
Otherwise you’ll want to copy everything in /var to another storage medium, reinstall (perhaps with a separate partition for /var then restore whatever parts of /var from your backup.