I would have had exactly the same conversation - or like to think I would have! - that you did. There is absolutely no need for a 7yo to know the intricacies of what happened. I think it's appropriate for a 7yo to know that some adults are not as respectful or considerate as we expect people to be, and that's not a good thing, but there's no reason for a 7yo to know more than that, or to understand how he and his science project played into that. Really - an adult being jealous of a 7yo's science project doesn't even make sense when you try to apply logic to the situation.