Here in the UK years back, unscrupulous growers sprayed the silicate-based additive used in road paintmarkings for reflectivity, as when applied to the buds it made it look like they were of incredibly high quality.

This was not scaremongering, I bought some myself. Twice.

I have connections with people in the old synthetic cannabinoid industry and know how cheap that shit is to buy and how easy it is to order from China, so I don't see in any way it being a stretch of the imagination to envisage people growing poor quality weed and adding to it.