Based on the in-game depiction, I think he means. Aside from a couple references buried in dialogue or in books to a jungled Cyrodiil, there's very little in-game to support that conception. Arena depicted it as forested and medieval, and Morrowind showed their clothing (though not armor, I'll admit) as being more reminiscent of 15th-century Italy than ancient Rome. To say nothing of the medieval European aesthetic of the Legion Forts and thatched-roof cottages. Unless the entire Imperial population of Vvardenfell, Mournhold, and Solstheim was from the Colovian west (Ok, the last one, I grant, is likely), it seems to me that the weirdness of Nibenay was only ever the fanciful artistry of the author of the PGE. Given that the average player doesn't hang around on these forums and has never read the PGE, it would have seemed to be something entirely from out of left field.
There's definitely some merit to this point; judging from Morrowind's surface portrayal of Imperials, you
wouldn't think that they resembled much of anything in the PGE1. But, it's odd: I came in with Morrowind, reading the books in game but not too seriously, forming all of my impressions on in-game material - but I was still somewhat disgusted with Oblivion, once the initial glamour of the thing wore off. I hadn't read
either of the Pocket Guides until last year, but the portrayal of Cyrodiil in Oblivion was still dissatisfactory. I don't know - perhaps its not so much what angle Beth chose to portray as how they chose to accomplish it. In other words, it simply lacked enough depth to make it enduringly captivating. Or perhaps it was just that there wasn't really any give and take between otherworldliness and more stock fantasy the way there was in Morrowind.
As for Nibenay: Colovia is described as the backbone of Cyrodiil. I'd assume that much of the Legion is Colovian, in culture if not blood. And aside from the Cult and the E.E. Company, all you see in Morrowind is the Legion.
I always thougth that "jungles" mean not only http://en.wikipedia.org/wiki/Jungle, but also simply "dense forests", "thickets". Difference between Valenwood jungle and Cyrodiilic jungles is huge. It was demonstrated in the "A Dance in Fire".
For example:
You see the contrast between Valenwood and Colovia?
That book took place after the "I do this for you, Red Legions, for I love you,", though, yes?
But still, I take your point.