I believe the term land bridge is different than sea lion.
Sea lion is a term used by the community to describe a specific attack.
Land Bridge was a term used by the company in the original A&A game (classic or 2nd ed) to describe action where you load and unload a transport from one territory to another without moving the transport.
Honestly, it is my belief the term land bridge has done nothing but brought about confusion. I can’t remember how many times I’ve had to instruct someone that the transport can still only move 2 infantry or 1 armor (in AAR it’s different, but I don’t remember seeing the term in the manual with AAR, it could be, I just don’t remember seeing it. Anyway, in AAR it would be any combo of two ground units provided at least one is an infantry unit.) And they’ve argued that a landbridge means unlimited movement on a transport.
Sigh….
Anyway, I personally just ignore the term land-bridge. It’s useless in my opinion. Transporting something is the same as land-bridging it except your transport doesn’t literally move on the board (but technically it does traverse the sea zone, just doesn’t leave it.)