I think the arguments here are weak. Using a builder is extremely common in API wrappers like this (I just did this myself wrapping an API in Ruby). In the second example, the code you pointed out was similar really wasn't that similar. Someone else made a good point: because this is an API wrapper there's really only a limited number of ways to do things.

Still, there's a good chance that someone looked at it to see how you did things -- these things are hard to prove. Regardless, I think your response is a bit over the top? Does it warrant this nasty blog post, or could you have just emailed the dude and said, "Hey, I noticed you guys may have been inspired by my code, a lot of appeared similar. I am licensing under GPLvXXX [or whatever your license is] and it requires some attribution if you guys did use some of my code." I suspect they would have happily given it to you. If they refused, well, then maybe then would have been the time for the rant. :)

No offense, but the way you handled this, you are coming off like some guy having a temper tantrum on the internet, instead of a developer with valid grievances handling this maturely.