This is a way of preempting the need to pay bump compensation by offering this to people who might accept it. Alaska Airlines do this as well:

https://www.flyertalk.com/forum/alas...el-credit.html

If they want you to change, but you’re flexible, you might do better just waiting and see if they pay you more to take a bump offer on the day itself.

edited to add: if you are comfortable sharing the exact flight number and date of the flight, someone here might be able to look up on ExpertFlyer (or you could do it yourself) to see what the loads are and therefore if it’s likely they’re oversold (but not by how much they’re oversold)