Being that was in the Keys, I'm surprised he was calling it "mahi" . Most down there call it "Dolphin" (Dolphinfish), and know it's not "Flipper." The restaurant industry started pushing the Hawaiian name "Mahi-Mahi" a few decades back so that uninformed people wouldn't think they're eating the mammal variety. The salty and fiercely independent people of the Keys said, "Screw it, we're still calling it "dolphin". " You'll see it listed as "Mahi-Mahi" in touristy areas such as Key West, ... but go to locals joints throughout most of the Keys, and it's still "dolphin." For what it's worth, very few call it by a 3rd name ... "Dorado".
Recently, the Admiral and I have enjoyed living in the Keys about 1 week out of each month. Most of the time, we are in Cape Coral in southwest FL, but the Keys are our getaway location. (Yeah, we know. Going from Southern Florida to even farther south in FLA. LOL!). A weekend here and there became 1-week each month. It's an addictive draw.