The Jet stream flows generally from West to East but can move up or down as it tracks. On that date it may have been flowing against the more normal great circle route (great circle is the shortest route with curvature of the Earth
Great Circle Mapper). Sometimes flying a ton more miles saves more fuel and time than bucking a 125+ knot headwind. SAN-BWI OTOH would want to take advantage of it.saving fuel and time. I can't find a source for past jetstream maps there's probably one out there somewhere.
https://www.wunderground.com/maps/wind/jet-stream
https://en.wikipedia.org/wiki/Jet_stream