Can't find more about this by Googling around... anyone knows what the crude message was and where it was hidden?
If you visited the url, it was just a hit counter. I found out about it on Sony's PS2 registered developer forum. Someone had put the disc through the PS2 "Performance Analyzer"[1] and had a peek at the VRAM. When I hit it site it was in the low hundreds. A few months later it was in the low thousands. A few months after that it was gone. konami.co.jp apparently isn't even a thing anymore.
[1]http://lukasz.dk/mirror/research-scea/research/pdfs/GDC2003_...
Previously they've had to deal with a piece of code that is designed only to work with the gamecube's L2 cache, and crashes emulators that don't emulate the cache layers close enough. Which emulators rarely do as it's prohibitively expensive; you're looking at somewhere between an order of magnitude and two lower perf. This code doesn't do anything in the good case, and doesn't have any reason to exist except to be an anti-emulation check.
Do you mean on nightly?
[0] https://tcrf.net/Meet_the_Robinsons_(GameCube)#Dev_Message