"What difference does it make?" is a good response.
The thing is, a lot of parents (especially moms) seem to have a thing about using their kids to compete with each other. Here's my analysis of the situation: these little competitions have all the gloss of a casual friendly chat, but under the surface, there's a lot of stress going on. I presume that they're driven by one-upsmanship in a strange hierarchy-by-proxy, where the kids are the unknowing competitors and the parents are the proxies for them. It's all built on a foundation of insecurity.
If the kids are all in a close-ish range of ability, the parents can compete away with a reasonable expectation that they can move their kids (and therefore themselves) up the hierarchy. "If I work with Johnny a bit more, I can get him to Sally's level and talk about it next week."
Anyone who's well outside the range won't fit in. If your child is behind, you might feel lousy when they're all competing and your child hasn't reached that level yet. IMO, they don't care about your child's struggles; they're only interested in themselves in this situation. Alternatively, if your child is well ahead, group insecurity might kick in, and the group will find a way to exclude you. Your child (and you by proxy) makes them feel bad. So if they get rid of you, they also banish the bad feelings as much as they can. Your kid just upset their odd competition. Reacting as a group and excluding you gives them a way to restore the equilibrium of their worldview.
Does my pop-psychology analysis make sense?
Personally, I don't have any time for this sort of thing. Blech. My strategy in situations like this is to just avoid the mommy cliques and find the people who aren't pecking each other. They're usually pretty easy to spot because they're alone or hanging out with someone else who doesn't fit in. Or I just bring a book, depending on my mood.