While ship assisted definitely seems highly likely I would dispute the idea that it was "trapped in a container" and not free to leave the boat. 
If trapped in a container it would be much more likely to have appeared in a location where the container was unloaded or at the very least opened. The fact that it was found at a location that was probably the first chance it got to fly off the boat to dry land suggests to me that it made the choice not to fly into the ocean on its way over but was free to fly off the boat when offered a real opportunity. 
Clearly I want this bird to be accepted by the WRBC. But apart from that I can't see how a bird would have escaped captivity as such a location. 

Chris WarlowOlympia
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman11.u.washington.edu/pipermail/tweeters/attachments/20191029/293eeb85/attachment.html>