i remembered the show just now. was it on national geographic? did it feature michio kaku at the end??
as far as i remember, they showed an animated picture of a process taking place in early universe where there was approximately one matter extra per billion(may be a larger figure) matter antimatter pairs.
and the light you are taking are the resulting gamma rays emitted from the annihilations.
you are absolutely correct(i think) and it is from studies of these gamma rays that scientists conclude that the dominance of matter should be traced to this asymmetry in the early universe.
and the existence of antimatter (made of antiparticles) is necessary as feynman has explained "to wed quantum mechanics with relativity."