Hard to believe no one appears to know what is going on here.
This is almost certainly “mineral classified” land, which means that the state school system owns 100% of the minerals, but the SURFACE OWNER has 100% executive authority and receives a 50% ROYALTY on all mineral production.
Essentially, the surface owner has a 50% interest in minerals and ownership cannot be severed from surface ownership.
So when they are offering you on your surface rights, they are really after your minerals.
This is almost certainly a SCAM and a low ball offer. A lot of scams are being attempted right now in Culberson County surface ownership, as most folks do not understand the basics.
Do not walk away. Run away.