Well, we do have a precedent for this as the other data that the UP transmits (not in the spectrogram) uses Merope 5C as its reference point. And then there's the COL 70 system which is used as the reference point for distance(?) or something.
The UA was also confirmed to be able to transmit location data over vast distances in a Galnet about 20 months ago. The logical conclusion for the target of this transmission was Merope - because it points there.
However - you have to wonder whether neither the UA nor the UP are actually sending their data anywhere perhaps (just broadcasting it and we're intercepting it) - and that it's the UL that does that. That would, however, completely contradict this earlier Galnet linked above - so... none the wiser really.
Also, just on the first point, as I read it very recently and to save anyone having to look it up; one of the pieces of info the UP measures/provides is distance from Col 70 Sector FY-N C21-3. The unit of distance used is the distance from Col 70 Sector FY-N C21-3 to Merope. 1 UPDistance = 871ly approx.