The person may know what is and how to use it without knowing its formal definition in programming language theory. I personally find interview questions that ask you to regurgitate definitions like an exam to be poor indicators of real world skills. It would better if the interviewer first established terminology to avoid confusion and then ask how they would use such language constructs
I don't think it's unreasonable to expect someone applying for an engineering role to know the technical terminology of their field. Especially if they've been "programming for many years" as this person has.
