there is no horno oven. Horno means oven in Spanish. It's like saying "salsa sauce".
EDIT: Probably the reason this happens is that most English speakers wouldn't be familiar with the foreign word, so the speaker uses it as a modifier to the standard English word. The listener doesn't need to know anything specific about the foreign word in that case and can just assume it's a type of the common item.
But also in Canada some uni-lingual English people may say "pont bridge" not knowing pont is bridge in French. Maybe uni-lingual French say the same?
"pont bridge" sounds like the exact phenomenon though. Does it have a more specific meaning that "bridge"?
But why horno-oven? Horno is oven in Spanish and just in one video someone mistranslated horno to "earth oven".
All the people besides all those 1.5k that saw the video will use the "horno" as "oven".
My argument is that it's not a mistranslation. In Spanish, "horno" means any kind of oven. In English, it means specifically an earth oven because when English speakers started using the word, they always used it to mean that kind of oven.
A sibling comment mentioned chai tea. It's the same phenomenon. Chai means any tea in its original language, but in English it means a specific variety and preparation of tea.
English is a bastardized language and has a lot of words borrowed from other languages. But once they're borrowed, they're English words and have their own meaning separate from their original loanword.
Sorry, I was not aware of this. Can you point me to another source, besides this video, that mentions the usage of "horno" as an earth oven?
On a more serious bit - the word origin of each is interesting. The word used depended on how it got to its destination - by land or by sea.
https://qz.com/1176962/map-how-the-word-tea-spread-over-land...
If it was shipped over land across the Silk Road, its name stems from 'cha' (茶). However, if it was shipped from the coast, the dialect spoken there pronounced 茶 as 'te'.