I believe he froze him because of the !zteling.
However it's suspect that he was doing the right thing considering another player in the previous map was !zteleing from zombies left and right and no action was taken.
And even if he was the ban is more than likely not just.
A rule is a rule. If someone else is cadebreaking you need to tell an admin. !ztele is not meant for humans to escape zombies.