I don’t know the actual numbers involved, but people are already jumping to the conclusion that it means 70% of customers are impacted.
“Affected” is doing a lot heavy lifting in this headline. The linked page states that a small number of customers are affects. So it’s 70% of a small number. Where “small number” is defined by Atlassian so we don’t really know the impact here. As best as I can tell my own usage has not been impacted at all.