No Eric founded Flutter at Google. However, Google had previously acquired another company called Flutter, and they had that domain lying around, and decided to use it. That's what I understood, at least.
Guess you're right. Establishing a "Flutter org" counts. Though, I've never seen folks in this space (Bjarne Stroustrup or Anders Heljsberg for example) say they're the "Founder" of XYZ language / framework.
I've nothing to add to the conversation, but I jump on this oportinity to tell you that i like the content you've made with Adam Barth on yt very much, have a great day :)