the Muscat extension dates back years - back to when Oman Airways flew F-27's and leased small 737's
To get there you normally flew Gulf and changed
BA offered a non change 1 stop
Oman Airways expanded and put in a nonstop UK flight
As late as 2006, IIRC, Oman still had a share in GF and it operated a non-stop LHR-MCT (in addition to LHR-BAH). Once Oman withdrew from GF and it became solely a Bahrain carrier so stopped operating this route. WY subsequently started LGW-MCT which later became LHR-MCT.