I apologize for how long you've waited for my reply... As Zera said, I'd had to take a short leave from opti.
This ban was not in fact in accident; I'd found a huge amount of grief by your friend Alex. Granted, this grief was partly the harvesting of a farm that did not belong to him, but the fact remains that there were over 400 blocks of grief found in the area. The scale of this grief is why the ban was set to be permanent.
I will pardon your friend when I log back in this afternoon because it was his first ban and you've both waited awhile for my reply to your appeal. Hopefully he'll keep in mind to only break his own blocks in the future.