Beef is the culinary name of bovine meat[0]. Calling whale meat beef is roughly equivalent to calling cow meat "pork".
[0] and afaik culinary names come from the corresponding animal's name in french: beef comes from boeuf (~ox, a castrated bos taurus male), pork from porc, veal is veau, mutton is mouton and venison is venaison (replaced by "gibier" in modern french).