I didn't say you screwed them over. I said you take their patch and use it to create value that you deny to the contributor. I'm not weaseling words here.

Some contributors will be okay with that. But some won't be - and you're misleading them by telling them that it's open source when it's not. When something is called "open source", it's assumed to meet a certain criteria - the OSD - and can be used as a mental shortcut. When someone sees that your software is "open source", they'll probably believe you - but it's not. You're taking advantage of that.