I actually didn't know about the change till we were about to leave. I was seated far from my son and I don't really watch him while he plays. I was curious about it because I thought the pairings were done by computer. It's really not a big deal, just wondering.
What causes a pairing to be changed?
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My son was recently in a tournament where his pairing was changed at the last minute (players had already sat down, written out notation sheets with info, and were about to start playing when the change was made, within 5 minutes of official round start). I don't think the change affected his result, but I'm curious as to why this would have happened. He was not playing a teammate and he did not switch from black to white. I don't know who initiated the change.
The director might have mispaired the round in some way and after the mistake was pointed out, was able to correct things before the round actually started. It is possible that somebody had misreported a result or something like that which caused the problem.
Don't you think you should have asked the tournament director at the time?