Indeed, the one in the vid uses bars just like you describe.

The audible tones you heard were likely to be something akin to harmonic overtones (or whatever the opposite of an overtone is). Each of those bars is like a bell. And like any musical device (bell, string, drum head, whatever), they likely generate a large complex swath of frequencies, only a portion of which are audible by the human ear. The TV set's electronics were tuned to pay attention to only the specific harmonic overtones which were the right ultrasonic frequency, with the lower (human-audible) frequencies being ignored.