Evan
My guess is that the car was jack-up when drained and not level, and there was oil left in the case. Warning only use GL-4 lube in the trans. Not GL-5 or GL-4/5 which can destroy the syncho's.
I've filled my trans thru the shift lever. But I would just drive for a short distance then re-check the fluid lever. Then add any more lube if needed. DaveW7