But what advantage is he actually gaining from throwing the flag if its going to be reviewed anyway?
Ok, I'll try to explain this but you have to remove yourself from this specific situation because the rule is applied to this qualifying situation, not written for it.
The booth only stops a review to take a closer look at the play if they deem it to be worthy of further review. (This is why coaches will call timeouts inside of 2 minutes to give the booth a longer time to review). Much like calling a timeout that he did not have, throwing a flag he was not authorized to throw is slowing the game to gain the advantage of giving the booth a longer time to review the play than they normally do.
Whether he was trying to get that advantage or just being inexplicably stupid is of no consequence. The rule is there to make sure nobody gains an advantage on that.