The three20 code has shuffled around a lot in the last 8 months or so, but if you look at the change log here http://github.com/facebook/three20/blob/master/CHANGES#L93 you can see that the maintainer, Jeff (who was a college student at the time and has worked his butt off on three20) is thanking a 3rd party for contributing that code.

There's attribution for other code in three20, so I think it's safe to say that Jeff didn't know.

It's also possible that there was simply a miscommunication somewhere along the chain. I wouldn't assume this is anyone being evil or devious until we hear the full story, and I expect the lack of attribution will be fixed quickly.