It is impossible for anyone to send an amount FROM an address they do not have the private key for.

If MtGox sent an amount from 16jM4mbzPQsPAxhbVk5pt9FAK9xCGm1m6m to SD for you
... then they did at some stage have the private key for that address.
If they deny that, then they are lying.

There are 2 'if's there.