Okay, maybe a little too campy with my framing that it borders science fantasy than science fiction, I know that stars are made of plasma which inspired that idea.
No, they are not. They are made of lightweight materials (hydrogen, helium, lithium and so on upto iron). "Made of plasma" sounds as stupid as "made of liquid" or "made of solid" does.
Interestingly enough it makes sense if fusion gun makes EMPs or electrocutes everything in the area since highly charged plasma is conductive (plasma is, well, ionized gas which is like gaseous salty water for electricity), usually is not charged evenly upon creation (some part is less ionized, some more) which allows current to be created and thus create electromagnetic pulse and slight electric discharge. On the other side you’d need A SHITTON of energy to perform something like that let alone create that much plasma in the first place.