"all attacks (even unarmed ones) made by the champion against xenos creatures count as having the toxic quality"

Does this mean a Deathwatch champion who shoots a xenos creature counts it is as toxic?

I just glossed over it the first time and kind of assumed it was only melee attacks, reading it again, I see it just says all attacks.

I would take "all attacks" to mean all attacks. The Champion is a master of hitting xenos where it hurts, or kills; makes sense that it would apply to all attacks.