"This is one study from the project" would make more sense in English.
אחד מתוך one out of (a group or collection)
Why not "only one research" ?
Because that's not natural English. "Research" is a collective noun. It's non-countable, which means you can't put a number in front of it and you can't make it plural.
Ze raq mekhqar ekhad mitokh ha-proyeqt.
What exactly does מתוך mean here?
"Out of", exactly as the translation says.
It's very odd English: it sounds as though the study was one of several removed from the project. I've reported it as unnatural (to say the least.)
I put "This is only one study within the project." which sounds better and was accepted.
Agree no one speaks like that
It doesn't sound unnatural to me. Btw, בתוך is within.
And מתוך is, technically, from in.
but=only, but not to Duo.