Yes, I don't understand that it either. You would think that when they scanned their boarding pass, that some alarm would go off or something.
Many, many years ago we boarded out AA flight in DFW at something like Gate 38A. Gate 38B had a separate check-in desk but boarded on the same jetway. One flight went left the other went right. I think the FA was joking when she said I hope you're going to SJC because that's where we're going. One passenger jumped up and said he was on the wrong flight, but it was too late. He wanted to go to MIA.
Using the common jetway to board two flights leaving close apart was the contributing factor here.
