It was for X-Radio originally, that's correct (which I've never heard because I'm not a Sirius subscriber). But seems odd that they would reactivate it, and cryptically, without there being anything bigger than something only-station-related. Then again..
Yeah, if it hasn't really been utilised since it was set up, or teased anything cryptically before, maybe there is something more interesting going on.
... But it would be so on-brand for the U2 fan experience to expect a new album, receive a cryptic text almost 5 years after the last album, only to end up getting a radio channel update