I remember that. I was in the same game and thought that he had found a way to hack into the servers, but the prevailing theory at the time was that he exploited a market bug which allowed him to place the same goods on the market repeatedly.

Those who made this claim stated that he executed this bug by using more than one browser to place goods on the market (same amount of units and same price) at the same time. Apparently, if this was done fast enough it would trick the server into putting all the goods on market but the player would only lose units in one of the orders, so instead of having 1 order of 1000 tech points on the market, he would have 2000 or 3000 tech points on the market, but he would only lose 1000 tech points.

I never bought that theory since it seemed too simplistic.