Yeah, that blog isn't right, or at least it shouldn't be. (Just because a DNS registrar allows you to set up @ to point to a CNAME, or www to point to multiple CNAMEs on their authoritative servers, doesn't mean that your recursive nameserver will know what to do with that.)

It might be that Namecheap allows you to configure "CNAME's" but actually implements them as ALIAS records or HTTP redirects or something similar and obscures that from the user. Not having a Namecheap account I can't say for certain.

GitHub is correct, the @ record cannot be a CNAME.