This is the problem with reporting these numbers. Virality works like a pyramid, the effect is felt throughout the whole pyramid, but only takes the top of it to set it into action.
10,000 facebook accounts with 100 followers who then have 1000 followers is very different than 500 facebook accounts with 100,000 followers who then have 10M followers.
It doesn't take many, social media is a far greater force multiplier than people realize. Just 12 people were behind most COVID-19 hoaxes spread online, and about 10 "superspreader" accounts are responsible for about 70% of "low credibility" tweets[0,1].
10,000 facebook accounts with 100 followers who then have 1000 followers is very different than 500 facebook accounts with 100,000 followers who then have 10M followers.