you aren't responding to someone proposing that cell phones cause cancer. they were refuting a weak argument that it is impossible, with an example of one kind of unanticipated interaction that could cause such an effect.

ie, saying that cell phone radiation doesn't cause cancer (or other negative effect) because the radiation is not ionizing, is a straw man- like saying that cigarettes cannot possibly cause cancer because the red glow of the cherry is also of sub-ionizing frequency.