Some of the comments on this post here: https://superuser.com/q/1034137/479461 are claiming this.
i.e. this one says (emphasis mine)
You got brute forced. This is why one does not leave a ssh server on the internet, even if you have a password. Anything short of key based auth is not secure enough these days.
– Journeyman Geek♦
I asked in a comment for clarification if they accidently are talking by "key authentification" about the keys of a keyboard. But got not even a response yet.(So since my private server actually has ssh root acces with an 2048bit encoded public/private key pair and thought it to be save, I'm a bit worried by this claim of an diamond user now...)
Is there anything to worry about using a 2048bit encoded key pair (as Journeyman Geek♦ claims) for ssh authentification as root, in case we assume no one has acces to the private key except me?