The cause of the brief surge of strong winds was a relatively deep low center that crossed northern Vancouver Island (see forecast below for 7 PM Sunday). The result was a very strong difference of pressure over NW Washington.
The pressure gradient over northern Puget Sound was enhanced by the impacts of the Olympic Mountains, which forced local high pressure upstream of the barrier and low pressure to its lee (see map). Look closely and you will see a lot of lines (isobars) over Whidbey Is. and the San Juans. That means a big pressure gradient, which drives the winds.
Here is the model forecasts of gusts at 7 PM Sunday. It predicted 55 knots (63 mph) over the water. Not a perfect forecast by a good heads up that strong winds could be expected.
Another good example of the weather contrasts we enjoy in our region.