This isn’t correct, you’re getting confused between StreetPass and SpotPass. Yes, SpotPass is a wireless tech, but it has nothing to do with connecting to other 3DS’s or Wii U’s (and the Wii U did not have StreetPass; only SpotPass). A StreetPass-like feature would be pointless on a Wii U because you couldn’t take it out of the house without it losing range from the console. The 3DS on the other hand, had both features. So yes, the SpotPass did provide you with “DLC’s”, but it did not have the same features as StreetPass.

Also, the users’ profile and their favourite game was shown in the friends list, which was not a part of SpotPass. I can’t remember for sure if you needed a Nintendo Network account for adding friends, but I do know that you can add friends offline through the local network, but this does not use the SpotPass network, as the SpotPass network requires internet (and most games which had SpotPass warned you of this prior to activation).

The local wireless connection used in the friends list is the same connection used in local multiplayer games, the same as how it works on the Nintendo Switch.