OK, I've got over 100 hours in the game and thought I'd seen it all as far as NPC behavior.
Today, I was walking up a path where one of the Khajiit drug dealers hangs. Just then, a Sabre Cat came over the side of the hill.
The Khajiit actually acknowledged the Sabre cat, saying "Oh, another cat" like they were old buddies. The Sabre Cat sat there a second, then they fought to the death anyway.

It was a great little bit of nuance and cool that Bethesda prepared a line of dialog just for this chance encounter (though I suppose if there is a Kajiit companion, you could hear that line quite a bit). After all these hours, its actually all the little touches that keep the game interesting.

I don't think he was saying that because he's a khajiit (as khajiit hate being called cats,) but rather because he had recently seen or fought a sabre cat (even if he didn't in-game)

I've come across a group of Khajiit a few times and never heard that line. And being a Khajiit I keep hoping for them to acknowledge me but they never do lol.

That's a good point. I do actually hate when the guards say: "Move along, cat" or whatever the say, but a lot of it has to do with their tone. Like theyre just waiting for me to steal something.