This study seems to ignore the fact that motorists also burn food energy and produce CO2 while driving. Wouldn't you need to add that to the amounts produced by the vehicle?
In any case, the publication is prefaced with this note:
NOTE
#1 : this is a back-of-the-envelope estimate of the marginal impact of biking or driving a kilometer, looking only at the fuel for each (food and gasoline). Our goal is only to stimulate quantitative thinking about what drives carbon emissions (e.g., transportation vs diet). It’s not an evaluation of whether biking or driving best overall, and it’s not peer-reviewed research.
The bigger issue is that the news media may present these "findings" in a way that misrepresents reality. In this context, "may" means "yep, you better believe they will". How is the normal citizen supposed to understand these complex climate issues when sensationalism sells better than a boring presentation of reasonable thought?