>Müller's identification became a minority position among scholars when it turned out that the people of Tokharistan (Bactria) spoke Bactrian, an Eastern Irania

>Müller's identification became a minority position among scholars when it turned out that the people of Tokharistan (Bactria) spoke Bactrian, an Eastern Iranian language, which is quite distinct from the Tocharian languages. Nevertheless, "Tocharian" remained the standard term for the languages of the Tarim Basin manuscripts and for the people who produced them.[11][16] A few scholars argue that the Yuezhi were originally speakers of Tocharian who later adopted the Bactrian language. And so forth. Not that Wikipedia is a reliable source in the first place but your link mentions a couple of competing theories, showing that we don't know - since all of it is speculation and unproven. Languages can be shared by people of different ethnicities. Many Europeans wrote texts in Latin and Greek despite being neither. To be clear I completely agree with you regarding the language, which is well studied thanks to the many preserved texts. We just don't know much about the people, even the name that was given to them was retroactively made up.