If you were a doctor, you'd be asked all sorts of different questions and probably have people things you wouldn't like to see(?).
This isn't an issue just for people who work with computers. If you have a job where people don't understand the specifics and limits of what you do and don't do they will make assumptions. Plus, people have a tendency to relate things to themselves. So if they don't know what "working with computers" means, I think it's more than plausible that they make the following mental leaps:
"You work with computers"
"I have a computer"
"There's something broken with my computer"
"I wonder if you can fix it (because I don't know if fixing it is something you can do or not. - And what have I got to lose in asking?)"