I mean, it was inarguably violence, and that violence seems to have a political motive (since changing or reforming the healthcare system is considered a political issue), and there is an element of using fear to further that end (since he would obviously have known that he cannot realistically change everything by himself or even just shoot every health insurance CEO, but shooting one while featuring a catchy phrase to make it clear the motive was being fed up with the health system, potentially makes all the other such CEOs and people in similar positions afraid that the next guy to try this might go after them next, and that more might be inspired seeing the shooting). Id argue that it does technically fit the term. People are just so used to that term being used alongside causes that they have no agreement with that they think it can never apply to a good one, or consider if it can ever be justified.