Yea is a download code. There is no way to download the game unless you update your system. You can't download anything on pc. I gave my brother the splatoon code and it will work on any switch. As long if it's a region code you might want to make a new account if the main account won't...
Just bought a 2nd switch for the heck of it and the splatoon switch came with 2.3.0 for me. Now the question is should I keep the 2.3.0 or 3.0 my original switch?