Seattle-bound United 757 flight from Chicago makes emergency landing at Spokane due to engine trouble
If this is the “rescue flight,” then it appears that not all of the passengers decided to continue on to Seattle. The news article said there were 180 pax and 6 crew members. Of course, we all know how accurate the news media is when reporting on aviation.
Just had a thought: maybe some of the passengers were actually going to a location between SEA and GEG. Getting alternate transportation to their destination from GEG would be logical and would account for the use of a smaller aircraft.
Another explanation is that a number of people were anxious about what had happened and didn’t want to get on another plane at that point. I was on a flight that landed early due to an engine problem and about half of the people were too shaken to fly out on the replacement aircraft.