I don't see that as proof the message came from Zenos. He's stranded on the end of the universe and
probably didn't think to bring a radio tuned to alien frequencies.
In fact,
the quest where that message is described to us indicates that it is Stigma-1's command to all of the Omicrons
I take it that the "powerful burst of energy" triggering the message was in fact Emet and Hyth flooding the zone with aether and allowing us to reclaim the Scions, which also seems to have affected other beings in the vicinity.
And Stigma-1 of course is the "leader" intelligence at least partly housed in M-017, who was spontaneously caring for the living tree and with whom G'raha had to reason to find our path forward.
It makes far more sense to me that the sending of the message was linked with unentangling the Scions – and perhaps the other beings – from the aether of the world once they were no longer required to hold it together. And certainly fitting with the earlier plot for M-017 to be sending that message.