Hate? No sh*t. But it's not labeled terrorism, because it's a white guy who did it.
Erm, plenty of white people and predominately white groups have been labeled terrorists before. The State Department proscribed all paramilitary organizations in Northern Ireland, as well as groups like the Red Army Faction, and domestically you had the Weather Underground and various neo-Nazi groups like The Order. Timothy McVeigh was also labeled a terrorist.
The reason this wasn't an action of terrorism is because it was the work of a lone wolf, not an organization, and the legal definition of terrorism applies only to organizations.