As you pointed out, he publicly denied those claims.

He also put his postal address onto the luajit homepage. And it adds up with his history at the University of Karlsruhe. You can find pointers that he was actually there in 1994, from old websites that survived the decades. His Karlsruhe e-mail address is even still being credited in linux's net/ipv4/tcp.c. The best proof I found that he's an individual is him being credited as supervisor of an academic Dipl. Inf. thesis that's still available on the wayback machine: https://web.archive.org/web/20000919224408/http://andy.rz.un...

I doubt that joking goes so far that you are mentioning a pen name on a thesis front page. In addition to the front page containing his name, the thesis also contains screenshots of websites the wayback machine hasn't caught in time that contain his name.