But didn't they? Or am I missing something here?

That's my entire point. The author of this book incorrectly wrote that for some strange reason. Go look at the second text page I scanned (11th line from the top). It reads "Kiara follows Kovu into exile, and they reunite on a snowy hillside that turns green as they exchange affectionate nuzzles." Not only that, the book also says "Zima" in place of "Zira" and implies Timon taught Kovu about Hakuna Matata. This man needed a fact checker.

I'm with Regulus. What's incorrect about that? Didn't they indeed reunite on a snowy mountain?