There's nothing incompatible with open source that he's doing. You get access to the source as well as the binaries, and much like routers running Linux, you can sell/force-donation software that's GPL'ed, so long as you give people the rights that the GPL entitles you to. Which does not include getting it for free. Just being able to see the source code, and modify it, so long as you then let others see your source code and modifications to those you distribute it to.

He's just making you donate before you get it (from him - if anyone else felt like putting it up, they'd be a bit dickish, but not really illegally acting), which, given that this project originally was a service purchased by someone else, for which he was promised a hefty amount of money, it makes sense that lxp would want to recoup that.

He wasn't really under any obligation to release it, and if he hadn't, we'd all still be sitting around either desperately clawing for the NeoPwn2 driver binaries, or hoping for more driver mods from someone else.