Indeed, it is—except that it could have been more strongly worded, e.g., “This is an attempted coup under the rubric of Soviet-style pathologization of dissent, based on armchair diagnoses that amount to, ‘I don’t like him; therefore, he is deranged and mentally incapacitated.’”
A coup is a sudden, illegal, usually violent overthrow of a government or political party.
The 'Amendment' part of the 25th Amendment refers to an addition to the actual US constitution.
It requires the majority of the Presidents cabinet + the VP (all hand picked by the president) to agree that the President should be removed from office.
Asking the VP to invoke the 25th amendment is not an attempted coup, despite what you may read in right wing media - they're just trying to get you fired up (and it seems to be working).