We, adults, rarely say "I was offended or offended by you." Probably, the whole point is that we have heard from childhood: “They carry water on the offended”, “They don't take offense at the fools”, “They fall on the offended balconies”, etc. That is a feeling of insult - it was a bad feeling, unworthy of a person. And we prefer to be offended silently, bated dislike in ourselves and cherishing this destructive feeling.
Until we had time to inculcate the same attitude to the offense to our own son or daughter, we often hear from the child that he was offended by someone, someone was offended at him or a confused story about mutual offense because of some kind of childish certainly a very important misunderstanding.
And it is important to explain to the little one that insult is not a bad feeling, but quite human, inherent in all the people around.
And the main thing is for your child to understand that the insult is his personal emotion. And the person who caused this emotion may well not want such a development of the event. And what's more, it may not even suspect that he offended someone.