Yea, that's not happening. My 100 Paragon barb doesn't even come close to that, and that's with botting 24/7.
I make 10m gold a day from just gold. A full day usually gives me 3/4th of a stash or so. Out of that pile, half is dropped on the ground, and the remaining loot is put on the GAH save for the one or two pieces that will go on the RMAH.
A 50M day is definitely possible however. Last week I had a day where three different items netted me $30 each. There's no way in hell he's making 50M daily on a consistent basis though.