In my eyes the ban and ban duration are fair.
You abused the trust given to you by the other player and stole their ME drives. The fact that the modify or access perms were set so that you could do this does not make a claim public territory, therefore rule #8 applies.
 No Griefing Any Protected Territory:
1st offense = 7 days ban.
2nd offense = 14 days ban.
3rd offense = 28 days ban.
4th offense = 60 days ban.
Includes everything that changes the environment of claimed land. Includes any block, item, action, liquid, that can bypass protection. Includes Griefing of own Town if other members did not agree and worked hard. Griefing spawn is a permanent ban.
as you can see, 1st offence = 7 days ban, so the ban will stay.