I think it's a round trip, based purely on the semantics of the question posed.

The question was not what kind of itinerary, ticketing, or reservation was made. It was what kind of "trip" was made.

According to dictonary.com, a "round trip" is "A trip from one place to another and back, usually over the same route."

The definition makes no mention of carriers, fares, or permissable stopovers.