. . . being a savvy businessman is a con man? There's loads to criticize about MS in the 80s and 90s, but buying DOS fair and square and then building an ecosystem around it was just a good business move. The stuff they got sued and almost broken up over is the sketchy part.
The point that he's a con man is that he signed a document with IBM to supply an OS when he had none. Of course in retrospect he was "smart" to go around and buy one, but in fact he was promising IBM something he didn't have and in an alternate universe he could be sued for that.