From what I understand it is saying that ivermectin is useful and efficient at blocking the tool (protein scissors; protease) that the virus needs in order to spread a protein out of the cell.
The new Pfizer COVID drug is supposed to do that too but ivermectin is 0.06$ vs new Pfizer drug with a 20year patent lots of cash for a good lobbying company :)
Credibility of the author idk :s