Earlier quoted context omitted.
You don't have to have a monopoly to be monopolistic.
The Sherman Act says that any action by an individual, or conspiracy of a group of individuals, to "restrain trade" or seek a monopoly is illegal. Monopolies aren't a prerequisite for antitrust action, they're the failure state when you should have acted sooner.
Everything is a monopoly these days. Its practically meaningless in these conversations.