Wasn't Hiro actually a Great Pyrenees? Saint Bernards have a distinct brown fur pattern with black ears, and a white muzzle around a half mask on their face.
Just gonna quote from the original post on here, since it explained this:
We know Hiro’s “Saint Bernard” breed in the art book is an error, since later he is claimed to be a Great Pyrenees. We’re leaving it in the art book as it is because it’s not a big deal and we don’t want to mess with the breeds despite obvious flaws, like Ken and George somehow being only saluki and great dane and not mentioned to be mixes, even though it’s a fact.
Hiro's breed changed in Meishoubu Retsuden to Great Pyrenees, which seems more likely, as you said. But for now we're just going on what Yoshi put down because it's not a common romanization error or anything.
Oh. Never mind then. I was just a little confused at first. Sorry.