This happened to me over a year ago on a flight from EWR to Central America IIRC... It was an identical card given pre-boarding by agents unrelated to UA! I don't recall if it was IATA, but there was a raffle for round-trip tickets (don't remember the amount). It was just a random event -- no issues, flight delay or cancellation. I'll admit it was different but didn't think anything of it afterward. I actually thought it ended long ago since I never experienced it again (until I saw this thread) @:-)