SARS, MERS, and now SARS-2 are all known for super-spreader events where occasionally one person just infects a ton of other people. And we know from testing that the amount of live virus in a person's phlegm can vary by many orders of magnitude so I guess that isn't surprising. There are a lot of people who infect just one other person but the overall R(effective) is substantially driven by the long tail.