I don't see calling someone a terrorist as a serious accusation, unless I put my legally binding glasses on. This discussion doesn't require them though.

Terrorist comes from "to terrorize" (click translations, word origin and more definitions), ie it comes from causing terror. To put it simply for you: to cause extreme fear. Given fear is a feeling, and has nothing to do with any legal framework, people are free to feel how they like. Whether I believe someone or others feels like this isn't relevant, everyone is entitled to their own feelings (as well as opinions). Free speech right?

I couldn't given a damn about the modern legal definition, as also I don't think this was the meaning or use of the word personally.