1. People who don’t know what they’re talking about don’t like to have that fact pointed about, especially if you use the word “ignorant” in context to the fact.
2. People like to confuse “pointing out the fact you don’t know what you’re talking about” with “being hostile,” because it makes them feel better about themselves. It’s generally not worth arguing to them that it’s not necessarily hostile to point out when someone doesn’t know what they’re taking about, but inasmuch as many people who don’t know what they’re talking about are invested in appearing like they do know what they’re talking about, and in the process of trying to make it seem like they do know what they’re talking about will make more statements that show their lack of knowledge, thus necessitating further pointing out that they don’t know what they’re talking about, it’s certainly understandable that they would regard it as hostile. And of course, eventually one may indeed become hostile toward people determined to continue to not know what they are talking about.