You're both right. Tesla doesn't make battery cells, they make battery packs. A battery pack is comprised of several battery cells, for example the Model Y has over 4,000 cells in its battery pack.
They certainly appear to be making cells now too.
https://cleantechnica.com/2020/09/22/everything-you-need-to-...
https://electrek.co/2023/04/21/tesla-update-4680-battery-cel...
Wow! That's huge! They're doing a good job of positioning themselves as being the world's best source of batteries.
Honestly, Tesla Energy is looking to eclipse Tesla as the main source of recurring revenue.
cells are not the same thing as batteries; it's possible tesla is making batteries with cells from Panasonic or whatever.
https://www.tesla.com/giga-nevada