I’ve even gone as far as to use NTLite to uninstall windows defender entirely. There are no programs on my PC that have the ability to scan (I prefer virus total, sandboxing programs, and of course glasswire). Yet GlassWire is still able to scan files, or at least claim it can scan files.
Most likely, it simply wasn’t programmed to throw an error if you don’t have anything installed that it can scan with. I actually tried to get glasswire to scan eicar (a testing file that will show as a virus on most scans, including windows defender) but realized that glasswire doesn’t have a way to scan a file that has never tried to connect to the network.