Quotes are also used to quote something verbatim, which is their more traditional role than "questioning". They're also used to refer to a term in a meta way -

Quotes are also used to quote something verbatim, which is their more traditional role than "questioning". They're also used to refer to a term in a meta way - like I did with the term questioning just now. In this case, he uses them for emphasis, like one would write "it's considered one of THE classics".