Facebook/Instagram need help please?

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In addition to my regular IG account, I made another (kind of a hate account, won't go into it...) Anyway, I realized it was stupid so I deleted it. A follower, and friend on FB, sent me an @ message on my regular account saying she knew the other account was mine (I think someone may have reported it, so I guess something got out) Then someone on FB, who used to be a friend on FB and follower on IG (not anymore) messaged me asking if I had created that account. When I made it I'm pretty sure it wasn't linked to my FB, but I guess it was? How do these people know this? Isn't reporting supposed to be kept private by FB/IG? I never got a message from FB or IG about anything. What's going on here? How would someone who's not following/friends with me know about this? How would anyone know?
Thank you Nancy. I cleared my history and cookies.
I know, it was stupid. I was just mad over some stuff...anyway, I still want to know how these people know!
If it was linked to my FB, still, how would they have known? Will anyone else find out? IG or FB don't go around giving out this information, right?