What is this about?

One of my lost boys, grew up and got married. I lost track of him for 20 years and just found him again a couple of years ago, thanks to a concerted effort by my daughter.
His wife is the most beautiful women I think I’ve ever know in real life! I’ve only been up to see them once so far, though.
They are black, and sometimes they post stuff that kind of confuses me (like videos of women violently fighting and getting all kinds of thumbs up and laughing emojis and stuff,) but I just scroll on by.

Well, his wife posted this today.

I said, ” I don’t get it…..”
She said, ” That awkward smirk. Lol”
I said, ” I saw that, but I don’t know what it means!”
She said, “Doesn’t really mean anything. White people just tend to be the ones that give the awkward smirk and other people find it weird.”
I said, “Oh. I read it as they all knew something that she didn’t know they knew and wouldn’t like it if she knew that they knew…..But they know.”
I kind of assumed, I guess, that they were all in the room when she walked in.

So..do you know what she is talking about? I mean, if I’m working and someone walks into a room, I’ll glance up with a small smile to just acknowledge them. Is that wrong? What am I missing?