AITAH for asking a question about racial grammar?

I can’t tell if I did anything wrong, or if my coworker jumped on something I said for the sake of stirring shit and getting me in trouble.

Background: I like to write and also be correct. Yesterday at work, I asked a coworker if you’re supposed to capitalize the B in Black when referencing a person’s skin tone or ethnicity. I actually asked an older coworker first, but I prefaced it by warning her that I was asking her because I valued her opinion as a person of the specific ethnic background in question. Idk if that’s kosher, but I like to be honest with people, and she’s always valued my transparency. She gave me her two cents on the matter, we had a little discussion, and all seemed well. I told her that I wanted more opinions because the answer might be different for younger Black folk. She understood and encouraged me to ask one of our other coworkers who is younger than me.

I went to the section of the office where that coworker sits (our office is divided by job title). But that particular younger coworker wasn’t there. I remarked on her absence to another coworker (Jenny). She asked me what I needed her for. I explained about how I’m writing a story where the white character refers to her best friend as “black.” But I don’t know whether to capitalize the B or not. Both I and Jenny are white. She said something about how you wouldn’t capitalize the P if you said “a Puerto Rican person.” I disagreed. She said, “okay, but what about if you said a portuguese person.” I told her I guessed I had seen it both ways, and I for sure had seen people leave “spanish” uncapitalized.

Now another woman sits in that section of the office next to Jenny. Her name is Kelly and she’s Black. So I decided to ask her for her opinion. She said rather succinctly that you would indeed capitalize the B. I said okay, thanked her for her opinion, and went back to talking to Jenny about grammar. I did remark out loud that I would like to have some sensitivity readers for my book, because all my beta readers are white and straight and don’t have other perspectives because they’ve never been persecuted for how they looked or who they loved.

I went back to my desk a few minutes later. Then like 30 minutes later, I get a call from my supervisor to talk to him in his office. Apparently Kelly had gone to her supervisor (different person from mine) and complained about me and Jenny talking about race. In my opinion, we weren’t talking about race, we were talking about grammar. But I apologized to my supervisor, we had a heart to heart, and I went back to my desk.

So now here I am, asking Reddit if I was accidentally insensitive. It’s hard for me to take Kelly seriously because she has complained about other coworkers for lesser things before. Also, she never said anything to me about whether my remarks were offensive or ignorant. So it feels like she just wants to cause drama and doesn’t care who gets run over for it.

If I am in the wrong, I would greatly appreciate a thorough explanation of how it was offensive. I get that asking someone a question about their culture can be a sensitive topic, but does it really warrant tattling like a child to an authority figure? I can’t ask Kelly to explain to me why what I said was offensive, because I don’t trust her not to make up more shit about me and get me in trouble. So I’d appreciate some feedback from y’all.