Also commented downthread, but we got extremely lucky then went the backronym route as shawabawa3 guessed. (I'm an engineer at FB.)
A more manageable 61 bits for 12 characters or so, from my recollection. Did you pile a dictionary attack on top of that?
I don't believe this does "break hidden services". That's just a truncated key fingerprint, not the key, and a collision would I suspect (but haven't checked) be a loudly visible error.
Actually, a name collision would still mean hijacking the traffic, even if they don't have the same private key. The last HS to announce "owns" the name.