AITAH for telling my friend how i found out about their new partner
I feel like a crazy person typing this because i genuinely don't understand what I did wrong.
A couple of weeks ago, a friend (A) told me their friend (B) saw our other friend (C) with a friend (D) we all know and like a lot, and they seemed couply. A asked me whether I knew anything about this, I didn't, but we agreed to keep an eye on C and D in future interactions to see whether anything was up. Recently, I've seen C and D together a lot and it was basically confirmed to me that they are dating (yay!!!)
Today I was hanging out with C and playfully confronted them about it, and they confirmed that they have indeed been dating D. C wanted to know how I found out about this, so I told them the whole story and situation. It was over-all just a fun, chill vibe.
I get home later with a message from A asking me why I told C about the conversation we'd had (C texted A about it). I was a bit confused, because I wasn't sure what the issue was. A went on to say how they are quite annoyed and surprised that I did that, and that they wouldn't have told me that B had seen C+D together if A knew I would tell C. I ask A if they want to call to clear up any misunderstandings because I was genuinely quite confused, and A responds asking why we would need to call about it, because it's "not that deep". They then say they are fine with it, just surprised. I am still feeling quite confused and uneasy about the situation.
Sorry if this is phrased in a complicated way - if anyone has any advice or input about this i would greatly appreciate it. A is a very close friend of mine, but I always get so stressed out with this kind of critique because I really don't want to be a bad friend: I am just really struggling to see what I did wrong here, as the details I shared to C were in no way speaking ill about A or B, or anyone, and it was just a fun moment between friends. A and C are also good friends.
edit: just to clarify, it's not C who is upset about this, C found the whole thing very funny. A is upset that I shared the fact that they gave me this information.