So I have no internet connection registered to my Switch, and I just got the update notification. Also, the same thing happened with that Mario Odyssey update...
How are they doing this without any available internet connections?
Well, I hope that OP don't care about some people's trolling. They can't see the forest for the trees.
Anyway, back to serious talks, Guessing about that's what you said, In my opinion...
1. Maybe you got the different revision software that contain the different update partition (that has higher than original release).
-> e.g) SMO v1.0 (the first release) has a 3.0.1 update, it well known public. but maybe SMO with version 1.1 (that recent release) could have more higher update than 4.0.0
Proof: Recently (After Dec 1), SMO v1.1 update released for few Asia(South Korea/Taiwan) country to support their language.
And it seems that some new revision-retail package has been released that day already contain ver 1.1 game update (and different update maybe, I can't sure)
2. Some kind of method that Ninty use system notification function that may alert the update is available even if internet was disabled.
-> e.g) like a check their own console when they met with another console and communication with that if that console already has a higher firmware - maybe similar mechanism like a Streetpass for N3DS)
Both of them possible, but First one is makes more sense to me that if you just put a SMO cartridge that bought recently. (After Dec 1)
(but If you not, and if you didn't leave out with console, I don't know what it really cause...)
Edit: Someone already posted that in forum here that new revision-Zelda BOTW that has 3.0.1 firmware that should have 1.0.0. So it's could be possible.
http://gbatemp.net/threads/warning-breath-of-the-wild-with-3-0-1-update.490651/
Edit2: Recently SMO/Console released in South Korea(Dec 1), and I've check that it has 1.1 game update that is already in it. (It doesn't ask for update even if I connect the internet.). And console firmware is 4.0.1. So maybe SMO with v1.1 revision could have 4.0.1 firmware I guess.