This is definitely an impressive result, but I'm pretty sure it was made easier by the opposite pattern. I've had a couple of TAs who I strongly suspected of being chatbots, even when I was talking to them in person. I'm still not 100% convinced they were human.
Another thing is foreign students and teachers who, even if otherwise competent, quickly get one used to language comparable with machine output. I think I may have been guilty of that at one time :)