I think you're confused about what the communication is.
The communication isn't the waving in "reaction" (it's not clear it's simply a reaction, but let's assume it is) to the original wave, but the original wave itself.
And the fact that it's also triggered by videos indicates it's not just a mechanical reaction (like some of the research about how plants "communicate" is which are essentially mechanical responses to stimuli).
However, this doesn't necessarily mean that the communication is meaningful. It just shows that a means of communicating exists.
The communication isn't the waving in "reaction" (it's not clear it's simply a reaction, but let's assume it is) to the original wave, but the original wave itself.
And the fact that it's also triggered by videos indicates it's not just a mechanical reaction (like some of the research about how plants "communicate" is which are essentially mechanical responses to stimuli).
However, this doesn't necessarily mean that the communication is meaningful. It just shows that a means of communicating exists.