The author has a very limited understanding of Buddhism - and as he even mentions, he has not studied Vajrayana, the higher levels of the teachings. Therefore he doesn’t really have a clue and frankly is just intellectualizing about what he does not actually understand. There are MANY completely incorrect portrayals of what Buddhism is about in those essays - based on his many wrong views and limited knowledge. This is a case of someone who failed to overcome the delusions of their own mind and instead decided to let it write essays about why that failure is not actually a failure. Nice try, but just digging a deeper hole in Samsara.
How is „ Vajrayana, the higher levels of the teachings“? It‘s one of three large subgroups. It would be like calling Catholicism the higher level of the teaching as opposed to protestant forms …
That's the traditional Vajrayana teaching. It claims Buddhism has three "vehicles" – "Hinaya" (a pejorative term for Theravada and its extinct cousins) being the lowest, Mahayana being the middle, Vajrayana being a highest. While obviously other Buddhists reject this, many Vajrayana still believe and teach it.
Rather different from Christianity. I've never heard a Catholic claim "Protestantism is the lowest level of Christianity, Orthodoxy is in the middle, Catholicism is the highest". That might not be a bad statement of how some Catholics think, but I'd be rather surprised if any Catholic would ever actually put it that way.