Where did I go wrong ?

If that is the reasoning, then that's fine. But I think something needs to be clarified:

What exactly are they doing that makes you think they have a condescending attitude towards you and your child?

Is it the mere fact, that they have prohibited their child from visiting your child at your house?

Have they said something to your personally that your were offended by?

Did they something behing your back that you overheard?

Do they walk a certain way, that makes you feel they are snooty?

Lets be more specific here. Lets try not to just label people as "condescending" just because they raise their children more strictly then you do. It is equally frustrating to strict parents when they are labeled as "condescending" or "more holier than thou" attitude just bcause they don't allow their children to do what other parents let their children do, when all they are trying to do is prevent mixed messages.