The question isn't posed as unsolvable. It's posed as being unreasonable to solve fully in a short interview setting. If someone gives you a challenge and says

The question isn't posed as unsolvable. It's posed as being unreasonable to solve fully in a short interview setting. If someone gives you a challenge and says "I don't expect you to solve this in an hour" and your reaction is to walk out, then you're unprofessional and likely the interviewer will be happy you left.