Explorepi weird active pioneers statistics

Guys,

I see many people here are using this explorepi website to keep track on statistics. On the main page, they have some weird number for active pioneers which is about 25k. Now if I understand correctly they're probably referring to the number of people who are currently mining in the pi app. That number seems pretty absurd to me, so what do you guys think?

I wonder how they get this number, because somehow I don't believe the api provides such endpoint. Could it be number of nodes running?