To be fair, the Coho salmon run at the Ballard locks peaks in September. It's possible you just had bad luck that day.
https://ballardlocks.org/fish-salmon-ladder.html
I run by the locks a few times a week and while I don't usually see fish, the presence of sea lions the last few weeks tells me that at least some salmon are running right now.
I'm assuming it was out of season because in talking with the Uber driver afterwards he said we'd missed the end of the season. I'm assuming his "local model" was up to date and accurate.