They sound alike in English but I'm afraid there's nothing more to it.
The tractate's name is מציעא,
which is Aramaic for אמצע (middle). Mem-tzadi-'ayin. It goes between "Bava Kama" (first portion of civil law) and Bava Basra (last portion).
Lost objects occupy the first part of Bava Metzia, but are not its sole (or even main) topic.