Tbh, I use variants of src and opt for where things get compiled / installed respectively too. I've been treating "misc" as more of a conceptual grouping for "packages whose presence and updates are not tracked in the system by other means" rather than as an installation directory.

E.g., you may note that one of the packages the script checks for is zoom. Zoom is installed as a normal .deb file that I download from the zoom website, and install manually using dpkg, which installs it in the normal system directories. But it has its own cumbersome update check mechanism (which involves clicking a menu in the app), and is not picked up by apt-update because it's not a repo package. So this makes it a good candidate for a misc-updates check, even though it's installed as a normal .deb file. :)