I think I found that post with the "Mia=Peace" information on the
German Zappybaby message board. The posters there are mostly expecting mothers discussing possible names for their offspring. No source information is given.
I checked: There doesn't seem to be even a single German-language website with information about given names (there are around 40 or 50 such sites) that offers the meaning "peace" for
Mia. Most do not carry the name anyway because it is probably very rare in Germany.
So it really is mysterious where the poster got her informations from...
Rene