How does getting defensive mean she doesn't know what real OCD is?

If someone pointed out to you that skipping songs wasn’t necessarily ADD/ADHD, wouldn’t you simply say, “Oh, it’s one of the symptoms I have. I’m diagnosed”?

I wouldn't. I probably would have just laughed it off with an "Oh well" as I did many times; it was a lot easier to do that than it was to open a discussion about ADHD.

People react different ways to things and not everyone reacts appropriately every time. They may have felt they were safe to joke about it with a friend - maybe that was their attempt to bring up a problem with a friend - and when they were shut down (or at least they may have felt shut down) they get upset and defensive.

But we could assume this and that all day. In the end, the phrase "just OCD things" does not a sucky person make and just because you'd never say it doesn't mean someone else in your situation can't.