> wouldnt it be clear that the away manager wanted the game to play off if s/he were present?

No, not always. The timeframe between the invitation and the actual match is very short, you may not react in time. I recall there was once when I noticed this "friendly" match (which is in fact anything but, since the purpose is to beat your players before the important match with challenger's friend) 30 seconds before the start, too late to cancel.