Yep, sure is, and I don't think early British 30th buttons have that design. The back of the button will confirm it if there's enough of the turret shank remaining. Regardless, I'm still quite convinced it's French.
PS: Being French is actually good news, because it makes it a Rev War button. It's definitely not Rev War period British, so even if it wasn't French it would date later 1790s/1812. The time frame of the French button also fits the Rev War period and even though the Dauphin Regiment has no record of service in North America buttons do turn up, and is the case for the one listed in the book. So in this particular case it being French makes it a better, more historical find .