I'm not saying this because the author of the books is Christian. I am saying this because they are explicitly relationship advice guidelines from a Christian religious perspective.
Most religions have ideas about relationships that are not informed by anything secular, and Christianity certainly does.
Opening a preview of the book I was quickly able to find lines like these:
"If we are willing to be molded by His hands, the Lord will shower us, our men, and our relationships with abundance. That is the way He works. He made us for each other. He is the Author of love"
"I feel like the Lord has blessed my desire to serve my husband and our marriage by giving me a permanent internal motivation to have a healthy "temple." And I know He will do the same for you"
So no, this is not the association fallacy. This is asking people to disclaim when the advice they are giving has a significant religious component.