I think it's a mis-label. OG Gameboys had the product code DMG-01 (acronym for Dot Matrix Game) and when talking about different models people often use DMG to

I think it's a mis-label. OG Gameboys had the product code DMG-01 (acronym for Dot Matrix Game) and when talking about different models people often use DMG to specify them or DMG Gameboy when the GB context isn't implicit.