The issue really is the tone my friend took - sorta of "so whatish", it is what it is.
When I read you're first post that's what struck me. Your friend (I'm assuming a good friend since you're discussing this with her) gave a possibly big thing a brush off. Almost as if you had said "DD is concerned grandson is bad at soccer", and she'd said "Well, it is what is, some kids just aren't good at soccer" which is true and not being good at soccer is nothing to be worried about.
But this could be something to be worried about. Or it might be nothing. If you'd been talking to me and I did know you're grandson, you'd get far too much information on how kids do speak at different times, some just take a bit longer, that there could be other issues at play, now is a good time to start looking into therapies but not worrying, and here are some agencies that can help your family. But that's because of work I do (and did) and work my best friend does. It's part of my world.
The next time you speak with her, I'd let her know that her it is what is attitude about your grandson was upsetting because you were seeking some comfort or reassurances. I don't think there is anything wrong telling someone what you're wanting from them. I'm not saying what she said was wrong, or that your feelings are wrong. You expected her to X, instead she did Y, neither of you are wrong, but as your friend you can (and should) tell her that you're looking for something more in X territory then Y territory.