Before reading the article I was wondering what do they mean exactly with PW managers supporting ln-auth.

Then I read this in the article:

It would be neat if our password managers could also do LNURL-auth. The Lightning wallet created in the password manager would be used only for web logins. This way you separate the payments wallet and the login wallet.

I mean, why not?

"Why not" is a terrible justification.

Why on earth would we need a LN wallet without any funds, incorporated in the PW manager just for logins?

It does not actually solve any issue.

It's like the author tihinks ln-auth tech is cool but does not really understand it.

Ln-auth is just automated key signing. You can solve the issue with logins by just using that, no need for a defunded LN wallet inside a PW manager.

The future I see for online logins is one where ln-auth is one possible source of key signing type authentication. Others would be HW wallets, yubikeys and PW managers themselves using their bultin cryptography.