Brigham Young's statement on Polygamy to women in existing marriages

I recently discovered the following website:

http://www.wivesofjosephsmith.org/

It details Joseph's various marriages, 11 of which were to women in existing marriage relationships.

I, of course, clicked on Sylvia's relationship with Joseph. One paragraph really stuck out for me:

Sylvia married Joseph Smith on February 8, 1842, when she was 23 years old. It is uncertain if her husband, Windsor, was aware of the marriage, but she did continue to live with him. Brigham Young taught that “if the woman preferred a man higher in authority, and he is willing to take her and her husband gives her up-there is no Bill of divorce required...it is right in the sight of God”. Brigham also explained that the woman, “...would be in a higher glory”. This may help shed light on Sylvia’s complex marriage arrangement.

I'm baffled by the terminology 'preferred' here. Brigham Young, the prophet of the church, seems to imply that if you are in a relationship, you may prefer somebody else and that would be ok to marry and sleep with them.

This kind of view seems so counter-intuitive.