If you read the full thing he's saying the autocomplete should not have filled in a referral code, only typing in the full address.

It's the same thing as when FireFox adds it's referral code when going to Google Search, I believe that's most of their revenue...

TLDR: the bug was the referral code was being added in the autocomplete. It should have only been added to the exact affiliate address, such as "binance.us".