They became smug after swearing the oath because they had taken some liberties with that oath that wasn't in their initial agreement.
For example, their initial agreement was that the god of knowledge wouldn't tell anyone about how to control the authority of the pathway of slavery, but Legion didn't want him to tell anyone else about how to upgrade an innate talent into an authority.
Another liberty that they took was to force the god of knowledge not to tell anyone anything about them, when their initial agreement was that the god of knowledge wouldn't tell anyone about them possessing other pathways aside from the three that they publicly claim to own.
But the god of knowledge didn't get angry that they made this oath. He agreed with them and swore that he wouldn't tell anyone anything about them and that he wouldn't tell anyone about how to upgrade an innate talent into an authority and use it to forge a supreme authority.
