I think I read that only the anode or cathode was solid state or something like that but not both. I'm too lazy to verify if this is accurate or not though so take this with a grain of salt.
But they are not true solid state batteries that much is true, hence the semi
If that were true, they maybe they got both the anode and cathode solid but they still need the jelly roll inside?
All I know is it's still requires liquid in some part of it that makes it not a true solid state battery, but it's closer and close enough to get away with using the word semi
Edit: and Tesla uses their dry coated elctrode (and maybe anode) process which is specific to them and that's not considered semi solid state. So there's definitely a difference somewhere