I was at one of the biggest marches for life in DC some years ago. Sponsors said half a million. I'd say at least 300,000. The press and the DC police said 50,000, and ran a picture of a small group of abortion supporters. Someone took an aerial photo, and it showed a huge crowd, maybe the biggest in DC history, but somehow that never made the news.
This is standard practice. If the Seattle police give out numbers, I'm sure they know which side their bread is buttered on.
I would question why the Seattle police estimated the crowd of an event in Olympia. You're right, though, if the Seattle police did this, it would be *very* strange.