And sorry to reply to myself but this is not great at all

I manually added the new RSA SSH public key entry to my known_hosts file (like they say in the blogpost)

Then ran ssh -T git@github.com and got

Warning: Permanently added the RSA host key for IP address '140.82.121.3' to the list of known hosts. Hi gassius! You've successfully authenticated, but GitHub does not provide shell access.

Then, when trying a git pull, I got this:

Warning: the RSA host key for 'github.com' differs from the key for the IP address '140.82.121.4' Offending key for IP in ~/.ssh/known_hosts:63 Matching host key in ~/.ssh/known_hosts:64

So basically, the Offending key is the one I added manually as per blogpost?

Ok, I am in Europe, and this seems like an issue of global distribution network or something, but this is not great AT ALL, either the blogpost information is not complete or something fishy is going on

UPDATE: The replies makes clear what I was seeing those errors and make sense. Thanks

EDIT: Formatting and Acknowledge of the situation per replies