What just happened?

[Travtman]

So me and my friend were on and there was a huge lag.  It destroyed half of his underground farm and changed the
mayors markets foundation back to cobble and took some away.  It only changed things at or below sea level (i think)
I'm not telling mods to fix it, I just want to know what happened.

[☣2crzy4uall☣]

My bet is a mod rolled back someones grief, and that person may have helped you build that area?