No, that is not true. Your own sentence use the word "most". In Indian there is a distinction between vehicle("yaan") and chariot("rath").
> We use the translation "chariot" because, at the time, the only vehicles we know of in the relevant culture were chariots.
How do you know? If the ancient text itself makes a distinction between "vaayu yaan" and "rath" then that indicates there were more than one modes of transportation.
>> No, that is not true. Your own sentence use the word "most".
This is a non sequitur. The claim was "flying vehicle" is a valid translation for what is commonly translated as "flying chariot" in most cultures, i.e. non-Indian cultures. (It's certainly so for Ancient Egyptian myths, for which, unlike Ramayana, we have contemporaneous sources.)
I'm actually struggling to think of a culture which (a) had, at the very least, chariots or something like them and (b) couldn't have some part of its ancient mythology properly translated as "flying vehicle." Maybe Sumerian?
>> In Indian there is a distinction between vehicle("yaan") and chariot("rath").
Clarification: in modern Hindi.
> Clarification: in modern Hindi.
https://kosha.sanskrit.today/word/en/Chariot/sa
You don't know Samskrut, do you?
Which does speak to their scientific knowledge, even absent an actual vehicle existing, given that their peers couldn't reason past "this thing we have on land, but in the air."