It goes a bit farther than that, even: IT work doesn't always equal IT work. Someone can be an expert in managing Linux-based load sharing servers and have no idea how to help a family member troubleshoot why their windows install is slow. Sure, they might have a better idea about how to start, but they'd be essentially starting from scratch for that specific problem rather than being able to apply any of their expertise to it.

Think of it like a programmer is a car builder, some IT people drive them for a living, others are mechanics. Someone who specializes in driving F1 cars might not have any idea why your car is rattling. The programmer might be able to figure it out if they built that car or the cause is something similar to what they see in the ones they have built. But if they build semis, odds are that isn't the case. But they might have a better idea than say a doctor.