How does that link relate to having a Gentoo forum? Was this all a wily ploy to advertise your question?
Far more efficient to simply reply to your own post and so bump it back to the top of the list.
I have never used Gentoo, but I would say that "emerge is not a command" means that emerge is not installed, either fully or at all.
Or that you need to do it all as root.
(PS please reply to my comment about the wiliness here and the emerge/grub in your other post. Thanks.)