CotS needed to swear fealty according to the info posted here [url="http://magicduel.invisionzone.com/topic/6619-children-of-the-eclipse-information-update/"]http://magicduel.invisionzone.com/topic/6619-children-of-the-eclipse-information-update/[/url]
So he did betray the eclipse.
Further, if someone asks you to join an alliance and send him an invitation, you know something more is going on.
He might not know what would happen after the invitation was send, but he can't claim to be innocent.