I think he is integrating Orsinium into High Rock, which he is slowly creating the landmass for, so orsinium won't be in skyrim's mountains, but rather high rock's so it is lore friendly
Orsinium IS part of Highrock. Every single iteration of Orsinium was in Highrock...... Orsinium may be considered it's own kingdom, but it isn't, nor has it ever been, recognized as it's own province.
The first Orsinium was in Highrock, not far from Wayrest. Then there was a second one, in a province called Wrothgar, between Highrock and the Reach. The one in Skyrim would be a third Orsinium. Or not, correct me if Im wrong.
Orsinium is located in Hammerfell in accords to the Lore. The last great Orsinium fell in High Rock by aid of both Breton and Alik'r alike because of piracy and other crimes. They moved to Hammerfell in the Dragontail mountains or some other mountain chain.
Check under location: http://elderscrolls.wikia.com/wiki/Orsinium
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4th iteration of Orsinium was in Hammerfell.
Then there was a second one, in a province called Wrothgar, between Highrock and the Reach.
The one in Skyrim would be a third Orsinium. Or not, correct me if Im wrong.
Check under location: http://elderscrolls.wikia.com/wiki/Orsinium