It's multiplayer only. They have some stuff in their FAQ about how playing vs AI is pretty different and potentially forms bad habits.
But I'd have to imagine part of it is they want to avoid any appearance of competing with the actual AW games that Nintendo sells. The focus on multiplayer makes it a very different thing from the cartridges imo.
It's a little overwhelming tho, given I'd never played vs humans before. Enjoyed vs my buddy, but against random people I've mostly gotten crushed.
If anyone here wants to run some casuals, I'd be down.