The copyright holder can do whatever they like with their code. They can multi-license it, add exceptions to the GPL for their own code, whatever. GPL restrict

The copyright holder can do whatever they like with their code. They can multi-license it, add exceptions to the GPL for their own code, whatever. GPL restrictions apply to you, since you're a third party, a licensee. You can only use the code in compliance with the GPL. So, if YOU take Amnesia's source code, and redistribute a binary, you MUST redistribute the source code as well. If you write a software "foo" that links to a GPL-licensed library, then "foo" must be GPL as well. This old trick was (maybe still is? I don't know) used by QT. There was a free, open source GPL version of QT; and there was a commercial version. You could develop and distribute QT-based applications as long as they were GPL; if you wanted to write a commercial, closed source applications, you needed to pay for a QT license.