Reasonable theory, but you have no evidence. You need to overlay the plane's flight path on the Whidbey area map, and draw a line showing the direction of view of the camera.
It would also help to set up a camera on a tripod, and take two shots 20 seconds apart, of another flight from SEA to an Alaskan destination. That would tell us if a commercial flight would explain the length of that contrail.
It is not enough to post one data point and then a theory. We need to do this properly with sources for any info posted like a photo, and solid logical analysis.
Too many anons on here are not autists, not serious, and only want to post ego-filled diatribes based on knee-jerk reactions. That may work with liberals who are used to value signalling but it does not work with us. We want solid reasoning, solid evidence. And we are not afraid to walk down many wrong paths and discard them when the hard evidence suggests they are wrong.