The 457(b) is non-qualified, so they can contribute to both.

"the 457(b) elective deferral limit is not offset by 401(k) or 403(b) deferrals. Thus, the maximum deferral limit of $19,500 may be contributed to a 457(b) plan, regardless of whether any deferrals or employer contributions have been made to a 403(b) or 401(k) plan."

From: https://www.captrust.com/navigating-the-number-jumble-403b-401k-457b-comparison/

The limits are different:

https://www.investopedia.com/ask/answers/100314/what-difference-between-401k-plan-and-457-plan.asp

https://www.irs.gov/retirement-plans/how-much-salary-can-you-defer-if-youre-eligible-for-more-than-o...

https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-topics-457b-contribution-l...

And when learning about them, make sure to pay attention to governmental vs nongovernmental. You didn't describe if that is a private university or state.

The 457(b) is referred to as a Top Hat Plan, and they can be a bit risky:

https://www.investopedia.com/terms/t/top-hat-plan.asp