Do they have the code for both? In that case, and if they're written by the same person, this can be very easy to determine, e.g. due to code reuse across projects.
Given that PHP is one of the most widely used languages for making websites, if not the most, that link seems rather flimsy.
While really valid, you also have to take into account what kind of hosting services are provided on Tor. Of course, one could host the solution themselves.
It was self-hosted. The only real hosting service ever on the darknet was Freedom Hosting, and its operator got busted (for having customers who hosted CP.)
IIRC, not just for having customers who did that, but that he KNOWINGLY hosted and let those customers use his services.