So if someone feels strongly about the way a module is written, he should be allowed to take someone else's idea and implement it as his own?!

Not exactly, no; and I don't think anyone means to imply that. However, there's a subtle point that I think should not be so subtle.

Open-source thrives on people feeling strongly about the way something is done, taking its core idea, and implement it in their own way. The fact that Mr. London seems to have used your ideas to create his own implementation is not a problem, and I hope you realize that varieties of implementations like that are part of how the community works. It may not be always ideal, but it's commonly an improvement (look at the X.org fork that's replacing the slow-moving XFree86 X11 servers).

However, it is considered inappropriate in the Open-source community (and just about everywhere else) to do something like that and not credit the original ideas. It's called plagiarism when one person claims another's ideas as his own.

That said, it seems like Mr. London's intentions were honorable, as evidenced by his willingness to hand control of the module to you -- you can easily update the docs to say something like "Mr. London's implementation of the ideas in Language::Logo, which were pitched by liverpole at a Perl Monger's meeting...".

Intentions aside, though, we do have a responsibility to credit others' work -- and that includes ideas, etc. that feed that work. The reward for contributing to Open-source is credibility and recognition; it's important that we as a community pay extra-special attention to making sure credit is given when due.