My wife did the closing on our place, so I didnt see it in person, but she assures me it did indeed feature a fancy electronic counting machine.
And since both the sellers and we were using the same bank, no cash actually left the bank- it was a 100% "white" deal, and the cash got rolled in, counted, shoved across the table like something out of a Dean Martin gambling in Vegas movie, then put back on a cart, and rolled back into the same safe it came out of.
Only it was now the sellers money, not ours.
The all cash thing actually makes more sense if its about sneaking around taxes and fees- but even in totally above board, all taxes paid on full price deals, the actual transaction takes place in cash.
Our experience was a bit classier, as we had a very good lawyer/escribano combination, who set everything up, and expedited in a quick and efficient manner- but the basic idea is the same no matter what.