Now, of course there's the possibility it was a fake, lol. There are a few visual cues, they have a different front clip, different rear bumper, the SRT badge on the rear gate, the air extractor hood, the big Brembo's and some other stuff you couldn't see at highway speed, like SRT on the seats and wheel...etc.
SRT:
Not SRT:
Now, of course you can buy aftermarket exhaust that will fit the GC that has factory duals and increase the pipe size coming out the back.
This is a V6:
And of course you can buy complete SRT replica body kits if you really want to be a posseur:
Jeep Grand Cherokee SRT Look Duraflex Full Body Kit 2011-2013
expressaerokits.com
I've encountered quite a few fake SRT Chargers around here. They always forget something, usually it's the brakes. They'll paint the callipers red but the size of both those and the rotors are way off.