Maybe a drop came off the clutch lever/piston assembly at the back of the transmission - possibly the boot back there has a crack in it or the clamp isn't quite tight? A bit of gearbox oil is supposed to get back onto the piston and bearings which are covered by that small rubber boot. Occasionally my R65 will let a drop of oil from there onto the floor after alot of riding. If you had your right boot underneath while putting it up on the centerstand that might have been what happened, perhaps?
If so, and it is only a drop or two, I wouldn't worry much about it. You can go in there and clean &lube everything and replace the little rubber boot&clamp at your convenience.
