Nope. The CHIM Talos used works retroactively as well. Cryodiil was never a jungle.
Yay for lore based retcons!
[censored] retcons. I want my jungle!
They use the same height-map so that hills, rivers, lakes and mountains are in the same places and they're putting points of interest, most likely ruins and caves, which it would make sense hadn't moved in the same places. They haven't outright said anything about the climate or vegetation.
Ruins being in the same place makes no sense -
especially not in the warm, water-rich climate of the Nibenay Basin. Caves make some sense, but only few of them; the rough structure of them doesn't usually change that fast, but details like "Is it reachable from the surface?" do. Rivers and lakes change
a lot in 1000 years. Most importantly though, the view of the landscape changes with the vegetation change; you just shouldn't be able to get the same kind of view from most surface-bound points.
Maybe from Kvatch, the top of the White-Gold Tower and Dive Rock, but that's about it.