I attend Great Ormond Street Hospital with my child and see a specialist in feeding/reflux/choking issues.
She has always said to me that ALL children up to the age of FOUR years old should have grapes and cherry tomatoes cut up.
That's because just like we can choke and cough suddenly at a meal on something after eating for 30 odd years, so can they. Grapes and cherry tomatoes are major causes of choking because when a child bites into one, occasionally there is a squirt of liquid that goes backwards and hits the throat. This causes a reflex that makes us breath in suddenly, which causes the food item to be sucked into the windpipe. If it's a whole grape, it's the perfect size for a pre-schooler to stick in their windpipe with no air getting round it. And they choke.
She says she has seen so many cases of normal healthy children of three or four choking to death on grapes, or getting brain damage from the lack of oxygen, or having had half their lung removed where the child has aspirated the food item.
So, no, I don't think your friend was over reacting. She was probably p*ssed off that a mother of a young child has left whole grapes out and wanted to let you know it. Not all children are "as good" as your child at eating, and some mothers know about choking dangers of grapes. I'm sorry to say that I actually think it's stupid, bordering on negligent, to give a party for three year olds (where some will still be two years old, or some will be younger siblings) and to provide whole grapes within their reach.
Sorry, but that's having spoken to one of the top specialists in the UK on this topic, and she always says to tell all my friends not to let toddlers eat whole grapes, even if they have been doing so for months.