I think he compiles it from pubs that openly post 'this month's boosts', or have a 'Boost Gallery'. I suppose sometimes it may just be a supposition based on a piece by an author with a normal following having 3000 claps from 100 people and 70 comments, which realistically is only going to happen if it's been boosted.

It's not fully comprehensive, as there's no way of getting that info unless editors release it, I don't think.