Why would anybody convert AAC to FLAC? Some people are just dicks.
I was wondering the same thing, and for a second I thought maybe it was done to strip the DRM off the m4a file. But I just checked, and Apple stopped releasing files with DRM earlier this year. Again, the whole thing doesn't make sense.
And wasn't it you that suggested that it may have come from a DVD in our e-mail group, or am I confusing that with something else?