I see I was mistaken, but I'm tempted to continue poking holes. Trying a different angle, though it may be a stretch, but could a caching layer within the VPN provider cause these sort of "too fast" RTTs?

Let's say you're a global VPN provider and you want to reduce as much traffic as possible. A user accesses the entry point of your service to access a website that's blocked in their country. For the benefit of this thought experiment, let's say the content is static/easily cacheable or because the user is testing multiple times, that dynamic content becomes cached. Could this play into the results presented in this article? Again, I know I'm moving goalposts here, but I'm just trying to be critical of how the author arrived at their conclusion.