What's the difference between a small and large beer at Applebee's?

The glasses Applebee's uses to serve large beers and small beers look very different. But in this video you'll see they are almost equally capacious.
When asked on Twitter about the revealing video, Applebee's replied thusly:

This guy has gotta leave some room at the top for some foam!
— Applebee's (@Applebees) January 14, 2019