Number of sales (or customers) is a vanity metric favored by startups looking to entice investment. Revenue is a metric useful for measuring actual business health.

Any chance the interviewer was overly exit eager ?

It is a startup very well known for being a loss-leader.

> interviewer replied "that's a dumb answer

a bit ot, but was that the actual response?

personally, stuff like this would have me ending the interview early.

That was one of the tamer criticism of my answers during my interviews that day.

I wasn't extended a job offer, but would likely have not accepted it if I had.

And what is your gentle phrasing for that action?

It's an interview, not a competition. The interviewer would've been much better of asking: "Why?"

I meant for excusing yorself.

I'd tend to go to "I'm sorry, but I'm afraid I'm wasting your time," for example.

Credit where due, I think this is the first time I've read of anybody being told how they got something wrong in an interview.

Why is that credit? Good interview questions don't have a right or wrong answer, they have a right or wrong process of coming up with an answer. Especially for a question like "Pick a metric," almost any relevant metric is defensible and has tradeoffs, and the question should be about how the interviewee analyzes engineering tradeoffs, gathers requirements, defends their initial proposal, and is open to counterarguments.

(If there's a correct answer, you can just give them a quiz. If there's a Googleable correct answer, you can just employ them and give them Google.)