It’s not that it’s inaccurate, because it is accurate. The problem is, that every conflict in Warcraft where there is a clear winner is technically adhering to the definition.
Think about every time you were sent out to clear out a tribe of Merlocs. You arrive in their space, and begin slaughtering all you see until you reach the requisite number of Merlocs slain, or you’ve collected some number of gruesome trophies you apparently carved out of their bodies. You’re pretty much a monster, but you’re okay with that because they talk like they’re constantly gargling mouthwash and look like frogs and fish had a really ugly baby.
Are the Merlocs hostile when you approach? Yes, but did you knowingly and purposefully move into their space to slaughter them? Also yes. You did a big bad genocide. You’re not there to kill only the “Merloc Dissidents” who are upset for whatever reason they have as free-willed beings—you’re just there to kill anything that remotely looks like a Merloc. You’re actively culling their population as some sort of deterrent against their interests.
More organizations on Azeroth are becoming multi-racial, but when it comes to most non-player races, they’re strictly mono-cultures which makes slaughtering them a deliberate systemic attempt to reduce their numbers, influence, in the world.
“But that’s war! They’re enemy combatants, so we don’t need to feel sorry for killing them to the last man/woman!”
Well sure. But that is known as “Total War” and if you feel that is justified when it comes to conflict on Azeroth, then you have to throw out any ethical issues such as the concept of genocide.
You can’t slaughter an entire tribe of sapient individuals and call it fair and just, and then when their neighbors get revenge by burning your town to the ground and killing the inhabitants you cry and scream about the horrible genocide they committed against you—without being a filthy hypocritical piece of garbage.