The AR-15 has been out of production since about 1982 or so, so I doubt if the listing is correct, unless RSR has started selling used guns, which seems unlikely. I do not recall an AR-15 ever being offered in 9x19 so I doubt that is the answer.
I recall that the AR-15A2 was offered in 9x19, but I am not aware that it is in current production except as an M16A2 sub-machinegun.
I suspect the listing is for what was formerly known as "Law Enforcement Only" restricted rifles made during the Assault Weapons ban. I would guess the "AR-15" nomenclature is intended to be "AR-15A2" and is probably a Law Enforcement Model LE6420 if memory serves (which it does less and less often these days). That would make it a desirable collectors item since "LEO" guns will be few in number compared to those not so marked.
Talked to a police equipment store back east who sold 25 of these recently. Colt had wanted these originally to just be sold to law enforcement. More recently they changed their minds. How many they made this year wasn't clear. The store sold their allotment of 25 instantly and has another 20 customers who want one. Colt told this store, however, that no more would be made unless there was a VERY large police order.
Bushmaster is introducing one. Any reason why that wouldn't be just as good?