Oh, so it is Nines. There was a theory I had seen somewhere that hypothesized that the riot trooper, as well as the stromtooper who died in front of Finn, were part Finn's training squad from the prequel book. They theorized that the one who died was FN-2003 (aka "Slip") and that the riot trooper was either FN-2199 ("Nines") or FN-2000 ("Zero"). Nice to know that theory was spot on.

They gave him an official name. Next comes him doing awesome shit in the EU.