No, it doesn't necessairly needs to be decryptable....
If you know what kind of hash it is and you know the list of your contacts, it is easy to encrypt all the emailaddresses of the contacts and compare that the the undecryptable hashes. It is also quite possible that he decrypted the map.dat (which is possible for sure).
EDIT: damn, I just saw you said the same
=>
unless TB found the algorithm and looped through all the contact names and compared?
Anyways the "ebty3yKWgtnJBg2W5B0m8yv7HoM=" name seems like a "normal" hash used by microsoft for all its services related to emailadresses and .NET passports and stuff. This is also logical in the sense that the other files in your Temporary Internet Files are listed as their equivalent URL's and stuff... And the CABLAHBLAH.BIN name (the actual filename) is just a random name AFAIK (except for the "CA" part and the extension).
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