SB is the only game I can think of with nonzero values for the last digit in score, and I don't remember anything that would be worth less than 10 there.
Remember how, in the past, there were optional comments displayed next to each stat? Players still have a chance to enter comments, but they don't show up. Unless you look for them in a database search...
It turns out the submission of 1 was accompanied by the comment "15,500 I am not lying, its a secret i found while playing the game that made me get a high ass score!"
I've changed the score down to 0, and if he tries submitting 15500 in its place then chances are there will be some explaining on his part in order.