Hypotheses:
> corporate VC that wanted to make a strategic investment
They want to put money in your company to make sure they don't have to compete with you or compete with someone else who might buy you down the line.
> They kept prodding around on the ML stuff, and how we might be able to use ML to accomplish roughly the same thing.
They're looking for secret sauce, barriers, friction. Something patentable. Something to keep others out and keep them ahead. Perhaps something that they don't think they can do themselves or maybe rip off when they realize it's useful. Remember Flux?[0]
They're investment thesis makes sense from this perspective: they're thinking like classic, amoral businesses.
Also note that if your product is simple and popular enough, people will likely make free clones. You'll need to be a good steward to keep your value.
Best of luck!
----
A bit of feedback: you need to be more transparent and up front about what how and why you're using analytics, and let people opt-in. I was a bit disconcerted to see you using Google Analytics in your extension without informing me.