Worked in a computer shop before, seen some warranties like first year take to the place you bought it, 2-5 years contact manufacturer. That being the manufacturers stance on the warranty, we would still look it up and help/advise customers if possible. Like if they needed proof of purchase we would print off a receipt for them even 4 years later.

In this case Best Buy is simply acting as a marketplace for other sellers. The items aren't sold under the Best Buy name, and it lists who the seller is. They're sold on the Best Buy website, alongside thousands of other sellers and Best Buy directly, just like many other retailers do. Companies like eBay, Amazon, Walmart, etc. all operate marketplace storefronts that third parties use to sell to consumers without having to have their own website and sales infrastructure.