If that's the case, then wait about 2 weeks, maybe even a month. If anything, ANYTHING out of the usual (Raised or lowered KDR from the last time you played, new name, more GP, more EXP, new friends on your list that you don't even know, all of these effects that you know you didn't cause.), forget about that NX gen. If nothing changes, nothing big, and you can still log into the account, then try your legit account, but still check up on the tester account to see if there are any extra effects, just in case something goes down.
And true, there are no 12 K NX cards. Most likely fake, but hey, might as well give him SOME info in case he's telling the truth.