He seems to resemble a Luminen, like the other character mentioned in the story. But when challenged about his nature, he says, no not one of those.
Perhaps he is one of the Stone Men, the creators of the Iron Men or he is partly one of the Men of Iron, some how sharing a symbiotic relationship with it's host. Who knows, Kron is certainly interesting.
Here's some links for you that might help you find out about the Men of Stone and Iron.
The Journal of Keeper Cripias
http://ifearnoevil.tripod.com/warhammer/journal.htm
THE BIRTH OF THE CULT MECHANICUS
http://web.archive.org/web/20120826151238/http://www.gamehobby.net/subject_indexes/subject_epic_40k.html
The later doesn't provide information on the Stone or Iron Men, but it does go into the Age of Strife