There is scientific proof that higher level elevations give you less oxygen, thus causing you (anyone) possible medical problems, not just having RA but healthy people too. Here is couple of links that might help you, can be a little confusing, personally the one from wikipedia was the easier to understand for me. Could your travel in general cause you a flare, sure could especially, but the swelling would have been from the elevation and lack of oxygen.
Hope you are feeling better now!
https://en.wikipedia.org/wiki/Effects_of_high_altitude_on_humans
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1114067/