I don't think it is. Neither in B2B and especially not in B2C. Although I think the consequences would mostly be worse for the customer, not the seller.

"Operator of buskill.in" does not seem like an unknown party?

It is. What's the postal address of the "operator of buskill.in" so I can file claims with him?

You seem to misunderstand what a postal address is.

The provided information on this website is not enough to do legally binding business (at least in some parts of Europe, it's not only Germany).

In Germany you can enter into a verbal contract without any exchange of personal details. Why would a website be treated differently? I'm curious.

As far as I understand German law is very flexible about what constitutes a valid legally binding contract.

Chapter 2 and 3 of the "BGB" contain several paragraphs which define legal rights and obligations for doing business via the internet or telephone.

§312f for example defines that customers must receive "a copy of a contractual document signed by the contracting parties in such a way that their identity is identifiable" (translated via DeepL).

A simple mail address is not an identity in German law, especially not when doing business with B2C as you always have a 14 day period to cancel your order (except for downloads and various, special products).

edit: If you want to cancel, you must be able to do so via (offline) mail, too.

Sure, they're not following the rules. Why would that affect the validity of your contract with them if you purchase good from them? Why would this contract not bind the seller?