Thanks all for the replies. In this case, I was a fairly key performer but I believe it is that company just doesn't want to pay any more. And they are happy replacing me with somebody else
Swift is just a language specification. It cannot be patented or copyright-ed. Anyone is free to make tools around the language specification. Just like there are many compilers for C/C++ on different platforms, we intend to make one for Swift on Linux/Windows.