Basically this is a story about a guy who was smart enough to script up his trading tool (he discovered that there is an API and wrote some code to use it).
He trade other people's money, using other people's (probably employer's) account and resources, I suppose.
His employer have paid all the fees, and, took all the risks - if there is profit - it is mine, if there is a lose - it is theirs.)
The essence of trading is about having a special (insider) position of even being a market maker, who just collecting fees from every trade other people do.)
But this is just my guess.