I can't offer an answer, but i very much understand your explanation.
My brother was at uni last year and lived in a house where the owner also lived there. Her rules were that any smoking, even outside of the house, was merit for an eviction. In the end he got evicted, but i was very much interested in the legality of kicking someone else on that basis. As you say, how can you prove he was smoking? Or you in this case. He could have been stood at a bus top next to someone with a igarette, and lost his house because of it, so far as i am concerned, that should be illegal.