Does your friend respond to other things you talk about/post? If this is the *only* thing to which she doesn't respond, then, yes, I think you have a right to be hurt. However, some people just aren't great about responding (and if you don't have a point for comparison, then you probably need to talk about something else ;))
Anyway, I think that there are many, many reasons for this and I do think it's possible to keep a friendship with someone who feels differently. I know that there is probably a lot longer story that you can adequately relay here, but your example didn't sound like a struggle to me and I can see how someone might have taken it as a brag, or just a chance to throw out there that he was signing up for a high-level class. I guess it's hard to say without knowing how you phrased it- was it just thrown into a long email or text or did you send her a note and say, "I'm excited/anxious/worried about signing ds7 for his first class. I really hope it goes well - I'm glad they don't give letter grades."?
I'm sure everyone has different levels of privacy, but honestly, I can't imagine ever sending out a text announcing that I had signed up one of my kids for a gifted class- just the nature of that seems to come across as bragging (I can't imagine doing it for soccer or karate or anything, so again, maybe it's just my own level of comfort with sharing things).
We happened to just drop our dd17 off at college this week, and I have mentioned to a few people who have asked about it that I was really excited about the Honors College- that they paired her with a mentor and it was a great connection and resource, but that was probably the first time I brought up that she got into the Honors College (she was accepted and given a scholarship back in the spring). So, if it comes up naturally, I talk about it, but otherwise I really don't.
You also have to consider that some people are not jealous or spiteful- they actually think that you're wrong. I know my MIL, for one, doesn't even think my kids should be in the gifted program, let alone doing a CTY class (not that it has stopped us- each of my kids has at some point done outside gifted programming). However, I know that she is actually trying hard not to say anything negative when I tell her my kids are taking an academic summer class, because she believes in kids having fun and thinks it's too much pressure.Obviously, we don't agree, but I try to respect her feelings and realize that she just has a very different view on it.
I know that some parents also can't help but compare. Honestly, one of my kids is bad at sports and sometimes I had to catch myself from thinking, "oh yeah, right..." when my sister would say things like, "(your nephew) is having a tough season in baseball" when I knew darn well that he had just played on the all-star team. For him, it WAS a tough year, but geez, when I had a son the same age who was still having trouble tying his shoes in third grade... so, saying you're worried about how your son will do might come across like you were fishing for compliments or something, because to your friend, your son seems like a super-genius. I remember a conversation I had about dd wanting to re-do her ACTs. A friend and I were commiserating, until I picked up on the fact that her dd got a 24. Mine got a 31. Our idea of needing to do better was wildly different, since a 31 was the 98th%-ile. Luckily, I had not at that point mentioned dd's score, and I didn't (I honestly thought that her dd would do similarly). However, it's just a minefield and I would cut your friends some slack.
THIS is the best place, or other gifted boards, or with your friends of gifted kids, to really discuss openly and freely. With your other friends, I would gauge things on an individual basis.

Theresa