The Old at Heart

An old woman just held the door open for me when I was brining my bike into a building and I muttered "thank you" to her as I walked past. After I was well beyond her, she yelled back through the closing door in a very snotty voice, "And you're WELCOME too!" So now I'm torn. Did she not hear me and say something rude to me for not thanking her, or did she hear me and it just so happens that when she talks she always sounds like she's in a terrible mood? There's no way of telling, but it hasn't been my first run-in with this woman, and I suspect it won't be my last. The best defense against very old rude people is to act super confused about everything, like whatever they're saying or whatever's happening is so out-of-the-world you have no idea what's going on. I suspect it plays into their notions that younger people are ruining everything.