The methodology is in the sentence you quoted.
If the whole premise of listt.xyz is showcasing financials of private businesses, I wouldn't trust the data integrity so blindly without at least some credible explanation of how those numbers came to be.
So, companies like baremetrics pulls this data from their stripe,paddle accounts. Business will give access to baremetrics/similar companies to pull this data. Listt uses data from this kind of sources.
This builds credibility around the business.