The reality is probably somewhere in the middle where, yes, the terrorist label does have some requirements. We couldn't go and call the democrats a terrorist organization even if we were politically motivated to do so. However, there are political motivations when we have two groups both killing civilians for political gain and we label one a terrorist group and not the other one. Vegita's advice is probably best where we give some weight to being labeled a terrorist group, but don't use the government's declaration as unquestionable proof (which then brings up the question as to why vegita would list off two dozen countries labeling a group a terrorist as acceptable proof). It's probably best to focus on the actions that each group performs, and the motivations they do perform them for, rather reducing what is occurring to a label like terrorism.