Call with the hiring manager.

I thought we had a good conversation. I received a call from the recruiter saying they would have to pass because I was not able to speak to certain aspects of the code. The problem was the manager only asked vague, qualitative questions with no follow-up on technical implementation or details. I even asked if there was anything I could expand on or clarify, and he did not seem interested in technical details, nor did he take the opportunity to rephrase his question. He just assumed his poorly phrased questions would elicit in-depth technical responses in a behavioral/get-to-know-you call.

If you want technical details (or really any question), ask the question in a way that tells the answerer what you are looking for. "How did that scale?" is vague and does not really get to the heart of what you want to know. "Can you explain the mechanisms you used to make that system scale?" conveys that you are looking for more technical details.

Either way, I would not want to work with a manager that expects you to be able to read their mind to figure out what question they are really asking, and even less so one that will not ask clarifying questions when it's obvious someone did not read their mind correctly.

Explain a project you worked on.

How did it scale?