have you people never seen an ocean? when you see ships go far enough out you see them disappear behind the curvature of the earth, you'll see masts of sailboats sticking up and the like.
None of what they say makes sense when you string any two parts of it together, so trying to figure out which thing is more mountain-like is giving them credit they're not really due.
No silly waves are on land. Have you ever heard of earth's largest wave? Wave Everest. A lot of people climb it every year. Sometimes they call them land waves to distinguish them further from water mountains.