My 50 cents...
When it is the mapper's wish not to see his work in another map, it should be clearly stated. I don't know from which map of Thunderbolt you used the decos but normally there's a ReadMe in the download file which should be always checked before using something from that. If there is none or TB didn't mention anything copyright-related, it doesn't make you look better (as you always have an "invisible" copyright when you put your own creation on the web), however, you have something up your sleeve you should point out to him if it is really so important.
Also, in a ReadMe, there should be a contact address (normally it's via e-mail). You said you had no contact to him... then google is your best friend
Really, you could've seen on which forums he is online.
One time I registered at some random (non ut-realted) forum, just to get in contact with that mapper (even if it was about another thing)! However, this requires TB always having the same nick name which is the case as it seems. Well, if you couldn't have found him somewhere else on the web, your decision to meet him during an online match would have been the best then!
Another point I always saw was "He should be happy that other people use his work so he can expand his popularity". But then: How are people supposed to spread a mapper's name when they don't even know that stuff was made by him when it is used in another map by another author who doesn't mention it?
That's why you must put the name somewhere in your download file. It's not really the permission that you need at all cost (unless it is explicitly stated in the ReadMe), but writing down who made it is a must, even or also when you want this mapper's work to be wider known.
And another thing: Even if this is a discussion worth to be stickied, please keep out any personal drama or opinions about persons from the public forums in the future.
so you take your chances with those ... just sayin