Yes, and in the context of the article: the 'pay for every computer' pricing contracts Microsoft pursued to its advantage were not by themselves illegal. They became illegal when used by a firm with monopoly power to stifle competition.

Unfortunately there's no bright-line rule that lets you know that today, you're a monopoly. You might write such a sales contract legally on Monday, and on Wednesday cross the invisible antitrust line which (after years of later largely subjective legal argument) obligated you to stop doing the same things that led to your success. So signing the exact same contract Friday would be illegal.