who buried the treasure in the first place (SPOILERS AHEAD)

I'm going to reveal a twist of the movie (so read no further if you haven't seen it yet) but at the end, the two guys get the treasure, though it was not what they expected. Instead of gold belonging to his grandfather who buried it when Romania turned Communist after WW2, what they found was Mercedes Benz' stocks from 1969, which they are able to cash in for more than a million Euros. My question is who buried this treasure, then. It couldn't be Adrian's grandfather since he was long dead by 1969. It is suggested that, since the property was turn into a seedy bar in the 1990s, perhaps one of the clients buried it there. So, aren't these two guys risking their life, by cashing in on a treasure that did not belong to Adrian's family, and was probably buried there by some shady characters?