">$100MM yearly" is, let's say, $8.5MM monthly.
">10,000 customers" is <15,000 (or they would have used that), so maybe 11,000 to 13,000.
That's around $650-$750 per customer per month.
"Hundreds of thousands of active users" means maybe 250,000-400,000.
That's 20-35 users per customer, when split between 11,000-13,000 customers.
That comes out to $21-$34 per user per customer per month, average (you can see pricing tiers here: https://www.pagerduty.com/pricing/).
(I don't know if they make money off contracts not available on their pricing page.)
Because of this, they are really at risk of being replaced in large companies that can fund a team to maintain a paging system as that ends up being cheaper than 5k licenses.
Surely this isn't some coincidence. How does one achieve this without some degree of sexism?
If they promise and deliver on a culture where women in leadership can thrive and attempt to recruit smart women, then more women will join. Success breeds success.
Companies that focus on seeking out qualified talent from underrepresented groups have a competitive advantage, by exploiting the inherent prejudice in their competitors to access an undervalued talent pool. This in turn attracts even overrepresented talent that is motivated to work for teams with these principles.
I've been on a team before where one member was adamant about throwing out resumes from white men for the sake of diversity. I know it happens.
So yes, the company probably did partake in sexism and discrimination to get there. Otherwise they are very lucky and a statistical outlier when it comes to qualified female applicants applying.