TBH I doubt the High King mentioned in Forge of Darkness was Kallor, as it makes no sense whatsoever. For one Anomander is some 300,000 years old and Forge of Darkness takes place when he must be have less than 100 years yet Kallor's empire was only some 120,000 years ago, 180,000 years after Forge of Darkness.
Besides that Kallor was the opposite of a "perfect liege, much beloved of his people", it's mentioned many times he was extremely cruel and hated, the crippled god was not called out of some basic power struggle but because they wanted to be rid of the horrible tyrant that making his people suffer so much.
Iirc it's also mentioned at least one other human empire existed over 100,000 years ago (though still far too late to be mentioned in Forge of Darkness) but mainly, the quote from Forge of Darkness makes no mention of the race of that high king so it could be any race and considering how not only the only known human empires were a long time afterwards but also humans probably didn't really exist yet but only their ancestors the Imass, it is even more unlikely that humans had anything to do with whatever is mentioned in Forge of Darkness.