It does seem like a "forgot to change tanks in all the excitement of First Solo" to me, although even if they started on tabs (typical) they should have around 1.5hrs endurance per side.
Having said that, on some Warrior II's' it's certainly possible to not quite swing the fuel selector across properly when changing tanks and, depending exactly where he was in the circuit when he swapped tanks (and what RPM he had set), it can then take a surprisingly long amount of time for the engine to cut. If he'd messed up a tank change during his downwind checks, the end result could look very much like what happened here.