TurboTax is asking if these contributions were optional (elective) or mandatory. If the contributions were optional, answer Yes. If these were mandatory contributions, answer No.
Thanks very much for clarifying. One last question: choosing yes or no doesn’t seem to affect the bottom line. Is this just an informational question?
I think it's asked in regard to the Retirement Savings Contribution Credit. This credit considers only voluntary contributions. If you don't qualify for this credit for other reasons, you won't get the credit regardless of the nature of the 457(b) contribution.