Gonzaga never lost to Washington. They played South Carolina close, and then lost to the Jackrabbits in overtime.
BYU on the other hand....did lose to Washington. I think a large part of it I just chalk up to BYU having an absolute terrible day shooting. Shaylee Gonzalez and Paisley Hudson combined for 4-27 shooting. I chalk a game like that up to BYU not figuring out a Plan B by the second game of the season with Shaylee Gonzalez just returning from injury. I also imagine that BYU was exhausted after dealing with a tenacious LSU defense the day before -- so just the perfect storm of Shaylee Gonzalez playing just her second game after her injury and BYU shooting atrociously.
You could call it a fluke, but in the last 2 seasons Washington has drilled San Diego, BYU and Portland. San Diego was tied for 2nd in the WCC last year, BYU is 2nd this year and I believe Portland is currently tied for 3rd. Maybe not a fluke? I don't know what other conclusion to draw than one of the worst Pac 12 teams would be more than competitive in the WCC.
Also BYU was 0-4 against Pac 12 teams last year. A few were close, some were blowouts. And they weren't the top teams. Arizona St., Oregon St., Utah and Washington St. (And the 3 years before that 0-3, 1-2 and 0-4; maybe they just don't match up well w/ Pac 12 teams).