Depending on what he said, I believe he is actually right, it is a phenomenon that happens bc of gravity.

Just like the water in a cup "sticks" a bit higher on the sides of a cup, the seas "stick" higher to where it is closer to landmasses, bc gravity is stronger there than say around the area of the Mariana trench, for example.

/r/explainlikeim5 may have a better explanation about it tbh.