>Why the downvotes?
Probably because it's inaccurate/exaggerated in a couple ways.
1. Genocide refers to humans, not animals, and requires the act to be targeted at a group of people that share some sort of traits (typically race, or cultural identity).
2. Disney imported "no more than a few dozen lemmings," which doesn't really meet the numbers the word typically is used for.
https://www.snopes.com/fact-check/white-wilderness/
Disney killed lemmings, and unless they attempted to wipe out all lemmings that share a particular cultural identity, it's probably pretty insensitive to use it in this context.