I love how you presented this talk, like I told you at the meetup I think you're a natural speaker and I'm sure you'd do very well if you decided to pursue that.
You already received a lot of technical feedback, but I would like to add that your talk was indeed a good bird's-eye overview of API development and it was technically strong too. Even if top-notch API developers (or sometimes just very "opinionated" people) might have a lot of technical feedback: don't be discouraged. Everyone is in the road of learning, but in every talk there will be a few people that already know everything you're saying and more. So it's not about making *them* happy: it's about bringing something to *the rest* of the people (usually the majority) who *did* learn something.
Anyway, excellent work!
I think the structure of the talk could be improved quite a bit, and I understand you've already been working on that. I'd be happy to provide some ideas if we talk privately. If you rehearse the talk a few more times it will also come out more fluidly, cause you had to think up a lot of things as you went along and that caused many pet phrases / sounds ("euhmmm..").
Having said that, I this talk was DEFINITELY worth hearing because it served as a useful reminder of several unit testing best practices, such as not relying too much on big setup tasks every time and using builders/factories/fixtures instead. I also liked the insights from unit testing in other languages (e.g. .NET) and most of the anecdotes you had about unit testing in other companies were both insightful and entertaining.