Considering there was a mass movement of people in 2014 to remove themselves of their Russian puppet leader, I'm not entirely unsurprised civilians are getting in on the action. Also Eastern Europeans are just built different, as seen with the Great Patriotic War, etc. For some of these guys, it's an opportunity to claim that same sort of martial legacy, to stand up against an invader. Maybe one not nearly as awful as the Nazis as evidenced by Russian willingness to not target civilians. But nevertheless an invader.
I know a lot of the guys itt are calling the Zelensky arming of civilians some sort of attempt to frame up civilians in bad ways. But to me at least, it's sort of the opposite. I think he's trying to ensure that if shit does hit fan in Kyiv, and they end up losing, the fighting continues after his death. And it also divests organisation away from the military, and means civilians can act as partisans and give the Russians hell after Ukrainian regulars are forced to leave. It'll still get a lot of them killed though.