Im not gonna argue whether pashtuns wore shalwar kameez or Punjabis, but here are some evidences that Kurta(slit shirt like kameez) and baggy trousers like shalwar were in fashion in india or atleast north west india since 11th century
Al Biruni states;
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So according to alberuni, shalwar kameez were in fashion in india.
there are also artistic depictions of kurtas and shalwars for instance
this figure is from gupta period, india, and one can clearly observe slits on both sides of the tunic the female is wearing.
secondly, the baggy trousers are depicted in an art piece from 8-10th centuries AD
https://www.nyu.edu/gsas/dept/fineart/people/faculty/flood_PDFs/Conflict and Cosmopolitanism.pdf
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it is clearly mentioned that the indian figures are wearing baggy trousers along with kurta.