R0 is a statistical average, but even if we assume that every person infects exactly 5.7 other people, these two tourists would have infected 11.4 people. Those 11.4 people would infect a further 64.98 people. you're already pretty close to 100 after just two levels of spread.

The only reason it's limited to as low as 100 is that people are taking precautions to prevent the infection from spreading.

R0 is an average metric. Averages are not your friend.

(don't downvote people who are asking a technical question!)

Some people will infect nobody. Some will infect one. Some infect 100.

5.7 would be the average (and it's an estimate, with many variables, some of which change from place to place and over time) of all these.

It includes infections indirectly caused by them (i.e. people infected by people who got infected by the couple), for as far as it can be traced.

I hope these people get to make civil claims against the couple.

The R0 is an average across many behavior profiles. These individuals engaged in exceptionally dangerous behavior and are the part of the samples that are above the mean.

Statistics, distributions, outliers. R0 is just the average value.