Re: Waht did I do to cause this??
Don't know your engine, but there is an upper seal on the gearbox that apparently has failed, or, as Harker said, you may have overpressurized the gearcase by forcing oil in without opening the vent. I'd bet that is what you did as you would have to put one heck of a volume of oil into that lower unit with the screw out to develop enough pressure to force it by the upper driveshaft seal.......and you would have oil everywere.
Mark