This year I’ve gotten about four that match what you describe. Before that I got maybe ten that were supposed to look like just normal people. Some of them often followed eachother.
They have all been on mastodon.social, which is what I first noticed and found weird. Personally I’m on a small and niche server being run by a dude in his garage. I barely have any followers and don’t post much. There’s not many ways to just randomly discover me on Mastodon.
It depends entirely on how you both communicate. I haven’t said it to my sister either and didn’t realise before reading your post. It’s all fine as long as you have a good relationship.