When I talked to a recruiter, I told him about my background and actually explicitly said "I'm not an [X] expert, I'm much more of a generalist" and went on to describe my other fortes. I mentioned it because [X] was listed as a qualification. I didn't mind "underselling" myself as the recruiter had reached out to me. I went on to an interview with two engineers, including the hiring manager, and they basically only wanted to know about my experience with [X]. I mentioned I'd told the recruiter that wasn't my focus area, but they seemed annoyed by me.
This is clearly a startup that doesn't have its hiring process dialed in, but it has me questioning how they plan to tackle actual, hard engineering challenges if they can't get something as simple as hiring down.