If the author owns copyright on every line of code used to make the binary, they can do what they like with it without need for a license. However, if there is

If the author owns copyright on every line of code used to make the binary, they can do what they like with it without need for a license. However, if there is other GPLd software in there, and they are relying on the GPL to be able to distribute it, then you are right, they need to comply with the GPL requirement to distribute everything needed to build it (Makefiles etc...). Disclaimer: IANAL, this is not legal advice.