My DS was doing half days for 1.5 years in the nursery, and nothing like this ever happened during this time (although I had plenty of other concerns for completely different reasons). Isn't it common sense to make sure that part-time children leave before other children start their afternoon activities??
My DD was also doing half days for about a year, and in the same way nothing like this ever happened in her nursery (a different one).
However in pre-school nursery which my both kids attended when they turned three, four-year olds were given lunch and stayed for the full day, whilst three-year olds had to leave about 15 minutes into the lunchtime. I thought this was very odd and unfair on the younger ones, but thankfully my kids didn't think of it as a big deal. Yet our neighbour's boy, when he started there, told me that teachers don't love him in pre-school, because they don't give him food! :( The pre-school was outstanding in every possible way with the exception of this awkward lunchtime timing.
In your situation OP, I would be very upset at the incident with the fair, and would think of it as wrong, avoidable and insensitive. I just wouldn't be able to help it. Still it is not a helpful reaction, because it is aimed at blaming other people instead of resolving the issue with whatever means you have under your control. So even if you feel like this, it's best to try not to inflict this thinking on your child. Just explain it the way it is - that her friends didn't leave her, even though it may have looked like that etc... Don't dwell on it either. I think there's nothing here worth raising with the staff, except the wrong phone number.