Okay, wait, this is great.
ESO retconned Heimskr into the latest in a long line of cartographers and historians, all of whom are called "Heimskr".
In ESO, Phrastus of Elinhir thinks that their saying Cyrodiil was a jungle was a mere transcription error.
Lady Cinnabar of Taneth believes that Cyrodiil was a jungle when the Ayleids (being from around Valenwood anyway) were in charge and that its climate changed over time when the Empire of Man was in charge due to the resonance of White-Gold Tower and its Stone, CHIM-EL ADABAL, with the Dragonborn emperors now leading the place (especially given that the first of them was literally the child of Cyrodiil--his dad did love unto a hillock).
Heimskr, however, has more history to see: the Pocket Guide to the Empire, First Edition, written a few hundred years after Phrastus and Cinnabar had both died (them being Redguards, who don't live hundreds of years). The Pocket Guide mentions the jungles of Cyrodiil, which does not mesh with Cinnabar's explanation and
certainly not with Phrastus's (which is completely wrong regardless).
So, what gives? This is answered in From the Many-Headed Talos, which Heimskr yells at you:
And after the throne of Alinor did finally break at the feet of Men, and news of it came to the Dragon Emperor in Cyrodiil, he gathered his captains and spoke to them, saying:
"You have suffered for me to win this throne, and I see how you hate jungle. Let me show you the power of Talos Stormcrown, born of the North, where my breath is long winter. I breathe now, in royalty, and reshape this land which is mine. I do this for you, Red Legions, for I love you."
What ESO did is retcon Heimskr into not just reiterating scripture, but
understanding it. When he says "Aye, love. Love! Even as man, great Talos cherished us. For he saw in us, in each of us, the future of Skyrim! The future of Tamriel!", these are not empty words; he knows what Talos did there, and why he did it, and what he was trying to teach us.
Remember that Talos filled in the place of the Ninth Divine, the Missing, Shezarr, Lorkhan, the Lunar God: their goals are similar, and
this is what that is.