If you are limited to one short question, a better choice is to ask them: "Teach me something technical you've learned recently." You can evaluate their answer on technical depth and correctness, communication skills, and timeliness of the topic. And if they can't think of anything they've learned recently, that tells you something as well.
I suspect you're largely filtering for people who are aggressively interviewing. When I'm deep into a meaningful project, I spend less time learning interesting technical bits. When I'm looking for a new job, I spend a lot of time learning random things that might be useful as a clever answer in an interview (because that's what so many interviewers want).
