And the reason you can't know is that he says nothing concrete, in the sense that none of his criticisms are grounded in examples.
Yes, the post is brief since it was written from notes several months after I had been talking to the rust guys. I couldn't justify the time to spend making the examples more concrete (and wasn't exactly encouraged to do so at the time). Sorry, that is as far as I've carried the load, you've got to take it from here.