I thought SP's put their ads on massage section so that it doesnt mix with all of the hundreds of fake ads on the escort section
In my experience, if someone advertises in the escort section, they are definitely not non-FS. I have never seen a SO that does not provice FS advertise in the Escorts area.
It's not, however, the other way around for the massage section, while a lot of the ads will specifically say "Non FS", many of the massage ads include mentions of FS options, etc. They do, as you suggest, advertise there to stand out from the fake ads, for sure.