Originally Posted by
MSPeconomist
I also noticed that they were returning to LAX after spending a weekend visiting mother in Canada, so it seems strange that they would be traveling on purchased one way tickets instead of using the return portion of a RT. Yes, they might have used one way award tickets in the other direction, or they might have purchased coach RT tickets, but when mother was so happy about the visit, she offered to buy them business class tickets for the return flights and let them discard the remaining portion of their RT tickets in coach, etc., but IMO these scenarios are rather unlikely.
The cow has offered some very good reasons, but I will also note they might also have flown up on WS. Maybe AC's flights were full on the way up so they flew UA LAX-SFO-YVR or DL LAX-SEA-YVR. Or they might have been somewhere other than LA and bought a one-way from there, either on AC or another airline. Like US domestic travel, transborder flights (CAN<>US) are typically priced as one-ways, with little to no pricing incentive to purchase round trips.