I think you might possibly find that in the real world...
...in the real world I think you'll find all sorts of things going on that don't line up with what you learned in CPL Met.
What you see here is simply sea spray kicking up on a windy day, usually (but not always) found in conjunction with a strong tidal flow (ideal conditions for breaking swell).
That clause on metflights site is an arse covering exercise, doesn't mean the radar cant actually see to surface level. For example, the Te Weraiti SSR on the Kaimais can see transponders down to 4500ft around GIZ and NPR on a good day (don't know why but certain atmospheric conditions help). That's way below direct line of sight. How? I don't know, the point is it does.