No, as other's have pointed out it's not. There are plenty of other areas to use it, even in other game engines. OP is just trying to make it seem funny by making the exaggerated narrative that it's the only use case for C#. If Boo was still around in Unity this joke would been accurate with that, don't think that was used anywhere else
For those wondering, it's most likely a jab at unity with it's new license model, as you could code in C# in it.