Regarding skills not being transferable. This is only somewhat true and the author is doing some goal post shifting here. What he said really only applies to game engines, not game frameworks and certainly not game programming in general. If you want to learn game programming and not a game engine, I recommend using something like Pygame or LOVE2D which are less prescriptive game frameworks as opposed to engines.
However, even with game engines, I have spoken with AAA developers who have worked with both Unity and Unreal and they all say the same thing. Game engines are a lot like programming languages in the sense that once you learn truly learn how one works, picking up a new one isn't that difficult.
However, even with game engines, I have spoken with AAA developers who have worked with both Unity and Unreal and they all say the same thing. Game engines are a lot like programming languages in the sense that once you learn truly learn how one works, picking up a new one isn't that difficult.