FMP file converts to FontBook on rename?

[Wickerman]

A friend of mine created a database of contacts in FMP7, based on one of the built-in FMP templates, which he named 'Filemaker Email List - Venues.fp7'. The file was on his desktop, in Mac OSX. He decided he wanted to change the name of the file to something shorter, so he rename it on his desktop the way you commonly do on a Mac, by clicking into the file label and just typing in the new name.

Somehow, in the process (perhaps he didn't get the .fp7 extension right?), the file transformed itself! Now, rather than being his database, it's converted itself to "Font Book" -- "Get Info" indicates the File Type as "UNIX Executable" while retaining his original filename. THe file cannot be opened by Filemaker -- adding the fp7 suffix doesn't work. If he opens it as is, sure enough, it's 'FontBook' with various system fonts in there. His database seems merely to have vanished.

What the heck happened? Apart from teaching him a lesson about back-ups, and perhaps suggesting that one is always better off using the "Save As..." command rather than duplicating in the finder, can we say what went on here? Any possibility of getting the original database back?

thanks

Albert