So something that can be used as a weapon in the shooting phase doesn't count as a weapon?
If it looks like a duck, and quacks like a duck...
IT'S A DAEMON! KILL IT WITH FIRE!!
If you look at the stats. Under weapons it says Gauss Flux Arc
Power matrix is not listed as a weapon. Under the power matrix entry in the lith abilities it states that the power matrix can't be destroyed with weapon destroyed results which makes sense if it isn't a weapon