Don't be. We wiped out their advanced scouting party with a virus. They might be somewhat peeved by that.
For me the UAs are searching for those Scouts MB has spoken about a couple of years ago now. It just seems more and more obvious that the UA are looking for something and seem to have found it. They scan every ship. And then transmit that in wireframe morse. In what way is that not telling us they are looking for a specific type of ship and just before Horizons was released, they found it - change in behaviour and point to location of discovery. Then we found the barnacles and we thought they were pointing at them so FDev added Barnies else where to make us question our conclusions. i.e. the Barnies are not what the UA are pointing at. Nor are the Barnies the thing that the UA have found. What do UA do? Scan Ships....
This is about what I'm thinking to.
UAs set up their shell in the summer of 3301. Exactly 150 years after the Mycoid bombing. They are looking for signals dating from 3151-3166. Why? Because they found out that the 'scouting party' survived. The Mycoid (probably closer to fungus than virus) only destroyed their technology. Hyper-drives in particular.
The Thargoids are looking for their 'missing'.
Barnacles are probably a 'plant' that the Thargoids brought for materials. Perhaps they even tracked down the Pleiades as the scene of the crime, by following the 'barnacle trail' from nebula to nebula? What then would we find, if we manage to follow the trail the other way?
Don't worry to much though, the 'Architects' are monitoring the situation.