The Ran quotes a machloeks in the yerushalmi as he does also on 49a between r' yochanan and r' yoshiya whether nedarim follow loshon torah or loshon b'nei adam (when they contradict one another). We always assume based on the bavli 49a that even r' yoshiya holds that nedarim follow loshon bnei adam. What about Brachos? When chazal are mesaken the nusach of a bracha does it follow loshon torah or loshon bnei adam? The Ran quotes a gemara in eiruvin 30a that if one makes a neder on "mazon" it includes all food even fruits. The gemara then asks that this seems to contradict rav and shmuel who say that mezonos can only be made of the 5 grains but not on anything else? The gemara answers that although "mazon" only inlcudes the 5 grains, if one woulds sy "kol ha'zan" that would include everything. This gemara seems to indicate that mazon would certainly not include fruits and the like, so if one made a mezonos on an apple, it would not work even b'dieved.
However, the Kesef Mishna (Brachos 4:6) writes that if one made mezonos on fruits it would work bidieved. The Nishmas Adam (58:3) justifies the position of the kesef mishna based on a Tosafos in eruvin 30a. Tosafos writes that the gemara only has a question on rav v'shmuel who say that mazon refers only to the 5 grains but not to rice and millet which indicates that even though we are koveia seuda on rice and millet, "mazon" only includes the 5 grains. But, according to the amoraim who we follow that mezonos is made on rice and millet as well, there is no question because although the term "mazon" technically includes all foods, chazal were only mesaken the bracha of mezonos on something that we are koveia seuda. Now, bases on tosafos that there is a machlokes amoraim whether "mazon" includes only the 5 grains or everything, what is the basis of this argument? It seems unlikely to the Chayei Adam that they are arguing what the loshon bnei adam of mazon refers to. Rather all would agree that the loshon bnei adam of mazon only refers to the 5 grains, but they argue whether "mezonos" in a bracha is meant to follow loshon torah (which would inlcude all foods but l'chatchila would be limited to foods that one is koveia seudah on such as rice and millet), or is "mezonos" in a bracha limited to what is loshon bnei adam as well, which would be only the 5 grains. Therefore, by nedarim where we follow loshon bnei adam only the 5 grains are included in "mazon" but by bracha where we include items that are called mazon b'lashon torah, it would include all food, just that the takana of mezonos l'chatchila was made only for things that the derech is to be koveia seduah, but bidieved since "mezonos" does inlcude fruit b'loshon torah and brachos follow loshon torah, mezonons would work on fruits as the kesef mishna paskens.