How did my friend get all of this monkey money???

My friend currently has 999,999,9999 monkey money (maybe a little less because he’s been spending it) and hasn’t spent a dime on this game. He’s only lv 36 and this is one of his new accounts (he keeps forgetting the password to his old ones) and he also has no clue how he got all of the money. Obviously not complaining, just curious if anyone else has experienced this or anything.