Yeah the NES Classic was sold in a lot of different stores. Best Buys, Walmarts, Targets, etc.
Actually, I think casuals were their primary target demographic. I think they were going after today's 30-something parents who may have played some Nintendo as a kid and wanted to relive that with their own kids now that they're adults. Current gamers are busy with modern gaming, and hardcore retro gamers already have all these games on the original hardware. Remember their best selling console to date is the Wii which was bought mostly by casuals and non-gamers. Its success, along with the success of their handheld division is what's kept them afloat.
But the bigger purpose for the NES Classic I believe was just to keep Nintendo fresh in the market and people's minds over the holiday season to bridge that gap to the Switch release. That was its real goal and now that its complete its a throw away for Nintendo. It may seem weird, but I think this is just how they think over in Japan. They certainly have a different way of marketing their products, that westerners simply do not understand.