That report was produced in response to a proposed Occupational Safety and Health Administration ruling that would ban smoking in federal workplaces. It found no basis for such a ban. The CRS also analyzed four other recent passive smoking studies. Two others showed no higher risk and a third showed only a slight, statistically insignificant risk. As is, that's something of a wash.
Surveys show that some people who claim to be nonsmokers are actually current or former smokers.
The EPA has recognized this phenomenon and has built in a small safety margin to account for it in the Fontham study. So the only truly significant positive study would have been rendered insignificant. Moreover, the CRS noted that the other three studies didn't allow for unidentified smokers. Had they done so, the lack of evidence for smoking's hazards to innocent bystanders would have been even more obvious. The ultimate purpose of the campaign that culminated in the EPA report was never to protect non-smokers but to harass and intimidate smokers themselves into quitting.