+1 fiction plate disintergrated or pressure plate fubar, wouldn't run it or try as you might damage the flywheel
Another poss is the clutch pedal fork has broken but you would prob feel that on the pedal
If it was the fork he would not start it in gear (or unlikely)
I would guess your first assumptions the clutch plate has split from the friction material so no drive transferred.
The other possibility is the primary shaft snapped but I doubt it is that.
Hope you get it sorted