His Chavrusa dropped him because he was a smoker (sug mentch) or because of the danger involved? If it was because of danger then he was being ridiculous, because what danger is there to sit next to a smoker after the latter washing hands and clothes (and mouth, I imagine!). My better guess would be that he was just giving an excuse, and didn’t like your friend!
If, however, he was dropping him because he was a smoker, and it wasn’t the smoking itself nor the after effects that bothered him, but rather the fact the fact that he was a Smoker (??? mentch), that couldn’t be classified as ridiculous, although it is quite a large statement on his behalf, which any smoker would definitely call unreasonable.