A good chunk of admins on UBP are retarded, let alone the majority of all admins in the game. Sad truth.
For the record, I cannot tell if you are lying or not (I'll offer the benefit of the doubt), but Guy had logical reasoning behind this. 'cookiemonster' must have had a bad reputation with Guy, and thus when he saw you, he thought 'cookiemonster' had somehow evaded the ban and decided to ban you. It was fault in his part that he did not atleast check or ask the whereabouts of you, but there was no cause for him to bother to check. Besides, in reality, how many admins out there are really going to think that far ahead?
None of this is your fault and hopefully this message will get out to others. You can try changing your name in case (Doubt you'll want to do that). Maybe its best to explain your situation to them on their forums or PM, but thats entirely up to you as there are other great servers to go on.
I wish you luck, cheers.