Yes, in saying an idea is patented I was technically incorrect - in theory, an idea can't be patented, an invention is only patentable if it 'teaches' how to implement it. Nevertheless, what is patentable is still a lot more abstract that an actual implementation.

So we have:

idea > teachable invention > implementation

(where '>' is 'more abstract than')

The GP seemed to by conflating the invention and implementation, in asking what difference the licence of made. That was the distinction I was trying to draw. Duda put the invention in the public domain, not an implementation - it's not clear you can apply the MIT or Apache licenses to an invention at all.