All of my children are at state schools.The eldest is at grammar with the middle to follow in Sept.
I suspect that the parents you encountered are representative of some
parents at indep schools but by no means all.
It's fear talking.It's believing the worst stereotypes of state school children.Hopefully experience will educate the ignorant out of their prejudice.
There is prejudice on both sides though too.Not all indep pupils are called Cordelia and own a pony.Not all indep parents are snobs.
My middle DD has had a hard week this week.She is the only child going to grammar and has had to deal with comments about her becoming a snob because she is going to grammar.
I have lovely friends whose children are at indep schools.I have lovely friends whose children go to the local state comp.People are a mixed bunch.
Harper Lee said" prejudice is born of ignorance and fear".We can only do our best to combat it when we encounter it.