Actually, it seems to use the initial and the final airports for each reservation. If it happens to be a roundtrip - then it will be ORD-ORD etc. I have a reservation with different start and end points, and that's what it shows.
Clearly a bug. But then again, reservations in the app never seem to keep a consistent name - every time I open it, they are all named differently (based on the first leg, the longest, whatever it wants to do)
And it shows a name of another traveler (one of the people going with me) rather than mine, on the main screen.
Also, for some reason recently reservation details take a lot longer to load in the app - as long as 1 minute.