According to the leaderboard on the Freebitcoin site, there are at least 2 referrers who attracted more than 100k users to the site and earned 28 and 27 BTC, respectively. It is noteworthy that there is even a referrer who has attracted only 6 users, thanks to which he received more than 23 BTC commissions.
Yes, that has been commented several times in the forum. The third one you are talking about was lucky enough (or knew how) to refer Big Whales, who are the ones who have brought him good money in referral commissions without him having to do anything.
At the current rate, it would be huge commissions, but as far as I know, the whole leaderboard was formed a long time ago, i.e. when the BTC price was relatively small.
Of course, the problem is that by giving the stats with bitcoin as the unit of account, the one who is earning money today by referrals and has started recently will probably never appear on the leaderboard because he will be earning much less satoshis than those who referred people the first years.