Look up the case of Standard Oil, against which an antitrust suit was filed, charging it with abusive monopolistic practices. The case was won, and Standard Oil was broken up - at a time when it had less than 70% market share.

no, they are correct
you are confusing "pure monopoly" which means a single firm has 100% share of the market with the general use and legal term "monopoly" which means that a single firm has control of their sector of the market