I actually have a DropBox account, I just haven't started hosting files on it... If they terminate my Mediafire account, I just might start hosting my files there on DropBox...
Maybe someone reported your links for no good reason; and Mediafire automatically warns if certain conditions are met? I doubt anyone actually LOOKS at the file; let alone checks its legal status.
Or, perhaps some new filter was put into place, which detected that your file met its condition.
Or, Mediafire is buggy, and something went wrong... D:
[Maybe their Terms of Service changed?]
It'll be interesting to see what they have to say, hopefully.
Actually...
Impersonate another person, whether real or fictional;
And more interestingly,
Upload any Content that includes code hidden or otherwise contained within the Content which is unrelated to the Content