Jeff, I don’t care what’s behind the foam. A fire from below would create the fumes so that is the area I would want it installed. Also the OP stated the foam is a garage ceiling, since we both live in Minnesota we know here a 1 hour burn barrier is the standard, I have seen double 5/8 rock called out also. Since I have never seen drywall inbetween or above floor joists I wouldn’t think of it although I have seen my share of self leveling gypsum flooring which is a great fire break.
Chuck, I know some inspectors quote code but I’m not one of them. Fear of litigation is also something I don’t bother with as I simply can’t live that way.
Regardless of how you or anyone else calls it I don’t think as a generalist I’m serving any good purpose by throwing code references at the buyer. Just a matter of preference learned after years of other people quoting code to me. I think code references confuse most people but if it makes an inspector feel he is doing a better report I say go for it. I prefer to report differently.