Google theory isn't doing it for me. I used to do Google ads for the small company I worked for years ago.
Doing some quick searches logged in and in America, I get an ad just searching for the full title, if I drop super, and if I change ultimate to switch (this one gives ads for where to purchase). If I add any other words to it, the game doesn't show. Why would this be? Because their marketing is only looking for when people search the game because it means you're looking to buy it. Search 'smash Bros dlc' and there's a Walmart ad for the fighters pass. This means they're looking to target keywords for people wanting to purchase, not those looking for other info. It's also likely because you get a lot of other content naturally, while searching to buy Joker leads right to the Smash DLC page as the number one result. They wouldn't buy ads for just these character names, as people are looking for how to play as them rather than purchasing the content.
This to me screams most likely fake and I'd bet it'll disappear soon because of the prankster hitting their threshold for the ad cost. This might be why it's only showing up for people not logged in too, so it's less likely to generate so it'll stay up longer.