He said he didn't mean to act the way he did, he was just upset with the other boy for not playing the game the right way.
My son is also a perfectionist who can be very impatient with other kids who aren't doing things "right." One of my new mantras is "it's more important to be kind than to be right." I've also caught DS trying to hide or talk his way out of his own mistakes, at which point I remind him "it's better to be honest than right." I've read recently that many perfectionists see being "perfect" or "doing things right" as a path to approval and acceptance (by themselves and others), so I'm trying to open my son's eyes to other pathways to acceptance, including being kind and honest. If nothing else, I want him to know that narrowly focusing on being "right" at the expense of other virtues won't win him any praise from me. Too soon to say whether this is having any effect, but his mental wheels do seem to be turning...
