Do yanks actually have cereal stalls at the mall? The idea of being served up some overpriced cardboard rings from a box that only costs a few dollars anyway at a food stall purely for the sake of convenience just reeks of America so I don't know if I should be surprised. No offence.
I've seen them, yes. Or SAW them, back when going to the mall was still a thing. They're not common, and like
@Aunt Carol says, they're almost always hipster spots.
The one that springs to my mind are Liquid Nitrogen cereal bars (often referred to as "Dragon's Breath"), where they sell you cupfulls of what are essentially Trix or Fruity Pebbles balls, doused in liquid nitrogen (sometimes other cereals too, but Fruity Peb-balls were the most common). The cereal balls come out of the liquid nitrogen bath smoking and steaming, and when you eat them, they make you blow smoke rings out your mouth, nose, and earholes. Apparently it was a fad in Asian markets, and got popular several years ago on Instagram, causing a minor moral panic and several thousand articles about how stupid Zoomers and hipsters are.


There are also "craft cereal" stands, which as Aunt Carol points out, are likewise rare, and generally sell their own, fancy, in-house cereals, meant to evoke feelings of nostalgia for Saturday morning cartoons or some shit. They probably wouldn't sell Cheerios at a place like that - they'd have something similar, only called FairTradeOs and served in a bowl of Sriracha - but you never know.
THAT SAID, yes, it is (or rather, was, back when malls still existed) possible to buy Cheerios at the mall. They're not exactly a popular mall item, but malls have tons of stores, and I'm certain you could find single-bowl servings of Cheerios there, somewhere, if you really looked. Once in a great while an ice cream shop will have cereal on the side (the idea is to use the cereal as a mixin for your ice cream, but I guess there's nothing stopping you from eating the cereal on its own), and a boomer store like a newsstand or a pharmacy might have a single-pack, maybe.
But it's definitely
not the sort of thing I've ever heard a person say they're going to the mall to buy. That's Lou being weird.
-edit- I'm looking through
Lou's local mall directory, and I'm not seeing anything that screams "Cheerios sold here!" It's possible that the Bubble Tea place sold liquid nitrogen cereal once upon a time, since bobba shops tended to be early adopters of that fad. But I'd be skeptical, since liquid nitrogen cereal is no longer popular (may even be illegal...?), and I highly doubt Lou would be culinarily adventurous enough to step foot in an East Asian bobba store.