The legend of the three "beasts" are that they were three pokemon who were saved by ho oh, those three pokemon were flareon vaporeon and jolteon, all evolutions of eevee and all cats, when reincarnated they might have taken a different shape but legendary kitties is unbefitting ao legendary beasts works best.
Nope, that was a fan term. Officially, they have only been referred to as Pokemon. Not dogs, not cats, not beasts.
Most places (like Bulbapedia) just agree on beasts because it's a middle ground. They don't do it because it's official.
I recall the GameStop posters for the shiny "beasts" event for HG/SS refer to them specifically as crowned beasts. Since it's GS and not Nintendo(despite being official posters), take with a grain of salt. --- Asketh Ky to Sol, "Heaven or Hell?" and Sol, being of Gear did say "Let's Rock." Roman Cancels 1:14