They are popping popcorn?
In this day and age it's already quite known that popcorn don't have it's own ability to pop lest there be an outside source for heat. The corn in itself is dried and has no sufficient water to be, for example, microwaved. The microwave popcorn bags have popcorn and fat in it, so that the fat will by the microwaves heat up, start boiling, and then the popcorn will be hot enough to pop. If I have understodd this correctly it means that what these guys are doing is to use the radiation concentrated from 4 cell phones against the popcorn, to make it pop. But I doubt it will even be powerful enough to compare with a microwave oven.
I might also have misunderstood the whole situation, both on what is happening on the video and the how and why microwave popcorn bags work. In that case, this is quite embarassing.