nicety

Hi,

But by the time we all said goodbye at the airport and she kissed me on the cheek and said, “Love ya, kiddo,” I’d recovered enough of my good spirits to realize her “kiddo” wasn’t just a knee-jerk nicety. I’d been given a seat at the family table. It was time for me to start calling this new world “home.”

(It is said to come from The New York Times, but I can't confirm that because I can't access the site. Here is a Chinese site about it.)

Does "nicety" here mean "being nice/kind"?

Thanks in advance!

No. It means a detail. See definition 1 here: nicety - WordReference.com Dictionary of English

The writer means it wasn't something she just said out of habit in such situations, merely because it sounded friendly or affectionate. She actually meant it.

The word nicety primarily means a small and usually subtle detail, but it’s also used in the context of what used to be called etiquette (nicety: “a detail or aspect of polite social behaviour”), and that’s basically how it’s meant here, I think.