No, unfortunately "USGI" and "mil-spec" are batted around pretty loosely in the AR world. USGI should imply used or surplus US military equipment, but it does not. Mil-spec just implies that it is made to one of many vague military specifications. D&H Industries makes USGI mags that are moly coated. Their teflon coated mags are identical dimensionally, but have a different finish that is not used "officially" by the US military. Both are marked with cage codes, which doesn't really imply anything other than that the maker has one.
However, and this is a big HOWEVER, the term military "issue" covers a lot of ground these days. All branches of the military now open-purchase everything from tools to clothing to weapon components at the unit level to supplement or replace more officially designated equipment. Thus, there absolutely are teflon coated mags in use in the US military, but they were purchased at the unit level or bought by individuals. Web gear, lights, sights, Motorola Talkabouts, GPS receivers are other common examples.
Edit: I forgot to add, $15.95 is a ridiculous price to pay for USGI mags. I haven't paid more than $10 for a new mag since 2004. Those $15.95 mags will be made by one of the same companies that makes the $8-10 mags. If they are teflon coated, more than likely they are D&H brand.