If the board members are acting according to their bylaws it’s not a “coup”.
But they were not, as the article said
As you note, the article said; however, the article did not show.
Was it a non-notice meeting? What constitutes notice under the actual bylaws, and what sort of notice was actually given? What constitutes quorum? Who was presiding?
If we had more facts, we might be able to draw conclusions one way or another, though given that Schafly was present and participating for the first 11 minutes, one might end up concluding that this is something of a mess. Facts would be useful things.
Under the nonprofit corporations act board meetings must be convened by the president and presided over by the president. Written notice of the time and place of the meeting must be sent to all board members and must state the issues to be discussed at the meeting. The notice must be sufficiently in advance. There are very clear rules for removing board members. There are provisions whereby board members can demand a board meeting and if the president fails to notice and hold the meeting they can then get a court order ordering the president to call the meeting.
But some board members cannot just privately get together and seize an organization.