This is something common in Oman, Omanis are known for being kind, generous and welcoming. So I'm not surprised .. I expected everything you wrote from the start.
1-It tastes MUCH better in UK. 2-Mild in Oman is very very very Mild. Even Medium in Oman is even "milder" than Mild in UK. 3-I never complained about the service in Nando's in Oman. I was always satisfied with it, and guess what? The "owner" even serves the people dining in.