You absolutely can ask it for code you plan to use as long as you treat chatgpt like a beginner dev. Give it a small, very simple, self contained task and test it thoroughly.
Also, you can write unit tests while being quite unfamiliar with the syntax. For example, you could write a unit test for a function which utilizes a switch statement, without using a switch statement to test it. There's a whole sect of "test driven development" where this kind of development would probably work pretty well.
I'll agree that if you can't test a piece of code, you have no business writing in the language in a professional capacity.
C# is .Net though. It's only syntax without it.
I think it's definitely a dig at windows, because that used to be the primary issue with c#, you could only really target windows and you could only write it using windows. You could run .net framework applications on Linux, but it was a lot of work and it really underperformed (which would fit the timeline of 2015, when this comic was first posted). Now with .net core you can make a self contained executable that can run on anything.