There’s perhaps a point to be made that using symbols instead of or alongside language is a good accessibility feature, but he makes that point only implicitly, if at all.
I'm not familiar with that particular hospital in Atlanta, and I think the panel could be improved. But in my experience working in hospitals, there can be really weird floor layouts that make navigation confusing in general, not just for elevators.
Hospitals also need clear communication for staff to increase response speed. If you say "Floor 3" it might be really unclear what floor on what subunit of what building you're referring to, but a color could be a clearly defined zone.
Part of what he's doing is holding up as ideal examples places whose architecture and use makes simple elevator control design possible. I think it's good to highlight elevator control design, but I have a number of issues with the way he's approaching the discussion.
The horizontal buttons might actually be useful for someone who struggles to reach to the top of the panel.