About 90% of the document is correct. The 10% that is wrong comes from making unwarranted assumptions based on how the Constitutional Convention of 1787 was called and how it operated. These assumptions are wrong because the original Convention was conducted under the rules of the Articles of Confederation, not the Constitution. The author also failed to read the American Bar Association's seminal 1973 document exploring how such a convention would work, how its members would be chosen, and how its purview would be limited by the state legislatures. Still, 90% isn't bad, and it's a good document to work from.
There was a very serious States Conventional Convention movement for the 17th Amendment. It was so serious that Congress was moved to take the matter into their hands.
So there is precedent that is more recent.