no, if MtGox exchange is short BTCs, the low price of BTC on mtgox is FAKE. there are no BTCs to be bought at $250. The price of $250 is probably
( (Actual number of BTCs on mtgox) * Bitstamp price ) / (Number of BTCs that mtgox is representing they have)
You are assuming that someone stole more BTC than MtGox total profits divided by $250 (see how a low number here helps MtGox?).
And even if this is still the case, like I said, they could borrow against the fiat they are holding for their customers.