How am I getting ads for products that I briefly looked at in supermarket but didn't buy?!

I was in the supermarket today. I picked up a product from a manufacturer that is fairly niche but has a unique memorable name. I spent no more than 30 seconds looking at this product. I considered buying it but ultimately didn't. My phone was in my pocket the entire time.

Less than an hour later I'm at home, I open FB and the very first thing I see is an ad for that exact product, from that exact manufacturer! …

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