In C# it’s certainly a label, it’s the same syntax and you can also jump to them with goto, which is actually very convenient sometimes. As far as I know this is an ancient feature and seeing how early C# was mostly inspired by C, I would expect it to behave the same way there.
Is “case expr:” really a label? You could put anything in there, like “case 42:”. I don’t see a label, but maybe I don’t know what a label is in C.
In C# it’s certainly a label, it’s the same syntax and you can also jump to them with
goto, which is actually very convenient sometimes. As far as I know this is an ancient feature and seeing how early C# was mostly inspired by C, I would expect it to behave the same way there.