I think the probability is about the same as finding a sha-256 collision in bitcoin 
So its probably silly to imagine it happened. Compare the chance of an inside job (someone told the thief where to look or told them the actual password) or a keylogger (etc) type attack was used to discover it, in such cases the fact one can find it in the source code is merely a red herring, whether deliberately dyed red or merely accidentally happening to be red.
-MarkM-
I didnt see a "lastpass master pasword " label on that string.
This.
Was ANYONE here even aware that the bitcoinica source code had been leaked, prior to genjix's OP on this thread?
Plugging the file URL into Google gives only a handful of results, with this thread being the earliest incidence of it, as far as I can tell.
That, plus the fact that the tar file appears to have been packed by username genjix.
Additionally, there's the fact that the lastpass password was supposedly the MtGOX KEY (username) and not the SECRET. A bizarre thing to do, which smells more like it's a fuck-up in an attempt to make up a plausible hack story.
The whole story is just too cute for me.