The authors are quite upfront in acknowledging their reversal of the normal scientific review process, stating that they are now submitting their methodology and data for peer review but felt compelled to share the results immediately in light of the pandemic crisis we’re facing. Make what you will of their analysis and results but their recommendations seem quite reasonable: for serious exercise, run or bike solo, do so in locations where there are no or few other people, and give a very wide berth (10 meters) to anyone you pass during your workout.