It's a spin off, so it's not considered a main game like new leaf. The game is exactly what the trailer shows, you're not a mayor and it's not an open town like before. I don't even think you catch bugs or anything. And amibo festival is also a spin off game
It's neither! It's a semi-mini-game that uses Animal Crossing elements with amiibo support. They don't have a good way to make New Leaf amiibo ready since it's almost 3 years old now, so they developed a new "game" that is one of the quirkiest in the franchise. Don't think it's part of the main series, it's not.