PSA: Don't tell Western doctors/therapists that you're a Leftist. The American Psychological Association (APA) classifies anti-capitalists, animal rights advocates and environmentalists as terrorists.
I'm pretty sure they're talking about people engaging in direct action like fighting with / firing on the police in opposition of an oil pipeline, or destroying GMO crops. The wording of the article is bad; I don't think anyone in their right mind would consider donating to an animal hospital or picking up trash in the park to be extremism.