yes, this key is an error, you can delete it. This tag come from boundary copy-paste mdg_adm_bngrc_ocha_20181031_shp.zip (link: https://data.humdata.org/dataset/cod-ab-mdg? ): 
admLevel = 4   is fokontany ( admin_level=10 ; admin_type:MG = fokontany )
admLevel = 3   is commune ( admin_level=8 ; admin_type:MG = commune )
admLevel = 2   is district ( admin_level=6 ; admin_type:MG = district )
admLevel = 1   is région ( admin_level=4 ; admin_type:MG = région )
admLevel = 0   is country
