What you do at your job during the day is usually imposed on the employee. Few employees get to choose the languages, tools, etc. that their company uses, so their interests aren't always relevant to their day jobs.

Your reading list on the other hand is entirely up to you. It's likely an indicator of something to the person asking the question. People who don't like math (or aren't skilled in math) aren't reading advanced math textbooks for pleasure.

I don't understand that either. I read papers, not books.