I don't think the horn has anything to do with it. The new EWS ring may have gone bad (new part # or old one?) or maybe the original wiring to the EWS was the problem in the first place and the replacement of the original ring affected the wiring enough to make it work again. Until you disturbed it when you did the horn. When your dealer checks it out, make sure they try a new ring before replacing the ring that is now in place.
My other bike is a BMW
RA & MOA #224