Weren't the initial Sellita models carbon copies of ETA movements? Certainly AIUI they're interchangeable dimension-wise, so some makers use either in a model, depending on which movements they can get for a particular batch.
I expect they’re just using what they can get their hands on. Normally with Squale it’s a 2824-2 but I’ve been wondering how long it would be before they wouldn’t be able to get ETAs anymore.
This is one of the nicer configurations of the 20 Atmos they've come out with. Dial is similar to the 50 Atmos but with a lollipop seconds hand.
https://www.gnomonwatches.com/products/20-atmos-ferrovia-ceramic