Connected to the Internet to activate a pre-loaded game?
You need an internet connection to verify your purchase to unlock the game. After that it is playable without any internet connection.
I’ve bought several pre-purchase titles on the Switch and the 3DS, both require a one time authorization from the Nintendo online store servers to unlock and play. Any time you try to run a pre-purchase game it will talk to the server to see if the authorization is available. Once given, it never checks again. Games are available at 12:00AM Eastern time/9:00PM Pacific.