It’s of no value to point out both can technically be implemented independently. That isn’t what happened, and even if it did it would still be user hostile.
The sorting algorithm that they choose isn't what makes a UI infinite scrolling or not, they're completely orthogonal. In MVC architecture terms they're model and view respectively...
Stop getting hung up on whether things are technically possible, and instead think critically about the actual effects of design choices.
The architecturally boundary between view and model (famously difficult to keep cleanly separated, by the way) is what’s orthogonal here. These are business decisions, not software decisions.