The Addon Manager is surely not "buggy". It MUST have some way to detect if you have a scenery handled by it, for the precise reason if it didn't, you would see bogus "trial mode" messages when flying on an area so, checking files for files belonging to a known product, is the only reliable way to not display such messages when not needed.
However, the method is not 100% foolproof. If, but a very unlucky chance, you have another scenery that has both the same name and the same name of a file we are checking for KSFO HD (which is so close to release, that we already have all support for it in the Addon Manager) AND its size is also within 2% of the file we are supposed to look for, you would see such message.
If you could contact me by PM, we can arrange you a Teamviewer session, so I can show you how to found this file, which might be useful to know, since we might want to change the file we are looking for, to be sure it will belong to KSFO HD and nothing else.