Was it insensitive of me to ask my friend's child to steer clear of my baby?

A friend organized a barbecue with several other families. When she arrived with her 4 year old son, she mentioned that he had been throwing up all day but that she thought it was probably food poisoning. As she was saying this her son was walking toward my infant--looking as though he intended to try to touch and play with the baby. I told him that since he had been throwing up all day I would rather he not touch the baby that day. My friend left and then told me later she was very upset with me because she felt unwelcome at a party she had organized herself. I told her I had made no comment about whether he should be there or play with the older kids....I just didn't want him playing with the baby in case he actually had a virus and not food poisoning. She said I should have spoken to her about the situation instead of talking to her child.