This example seems… bad to me. Are you simply saying that light moves slower from A to B through a medium like water because it takes a path that is less direct to navigate the medium?
Edit: wrong one https://youtu.be/yP1kKN3ghOU?si=hsBj0RpzOb3JZWdS the one above is the "why."
That or you misunderstood the physicist. You need to watch both videos to understand what's happening here.
The speed of light is not "slower in water". Light propagates more slowly through water. The subtle difference is not just pedantic semantics. It's the key to understanding how we don't have a paradox on our hands.