It's a 26" indeed. But how "small" is he? Even 26" bikes come in sizes for tall people. ;-) My Ritchey is size Large (I'm 1,82 m).
Oh dear....you clearly haven't been keeping up with corporate 29er marketing B.S. ........26" is for children, dwarves and shopping bikes.

Unfortunately, I never got the memo either, so I've only ever ridden 26" at 6'4" tall...
Good luck with the sale its a fantastic bit of kit.