Is he being silly, or does he have a point?

Our youngest is 20 months and up until a couple of months ago, she always called my fiance "daddy" but now she calls him "papa." We have no clue where she picked it up from, but I think its kind of cute. Her daddy doesn't. He's been encouraging her to call him "daddy" again, but she keeps calling him "papa." I asked him what was the big deal and he said that he doesn't like being called "papa" and would prefer it if she called him "daddy" again. I think he's being a little ridiculous. Its like we spent all this time telling her to call him "daddy" (you know since everyone in our lives doesn't refer to him as "daddy") and now she's developed something else to call him which I think is sweet. I mean, its not something crazy or anything. He wants me to encourage her to call him "daddy" again, but I don't know if that would be best. I mean he doesn't hate "papa" but he doesn't love it either.