The article says the website doesn't need to know your date of birth, that the state will issue you a certificate once you're over 18. Since many people I think will do that as soon as they can, it's easy then to see patterns of "this person created an account on age restricted websites with the same email address, they didn't have one before, therefore they probably just turned 18".
I find it also sad (and maybe a bit suspicious) to see someone that has blogged since 2003 use AI to generate blog articles, especially for a controversial law that has been pushed again and again in undemocratic ways.