From one of the secondary references in the linked study (thanks, Tom):

Conclusions.— The conclusions of review articles are strongly associated with the affiliations of their authors. Authors of review articles should disclose potential financial conflicts of interest, and readers of review articles should consider authors' affiliations when deciding how to judge an article's conclusions.

Analysis of 19 epidemiological studies shows that people who have never smoked have an estimated 30% greater risk of ischaemic heart disease if they live with a smoker (P<0.001)

This is surprisingly large—almost half the risk of smoking 20 cigarettes per day even though the exposure is only 1% of that of a smoker

The excess risk from smoking one cigarette per day is 39%—similar to the risk in a non-smoker living with a smoker

The effect is mainly explained by a non-linear dose-response relation between expsoure to tobacco smoke and risk of heart disease.