"All Pokemon attack, therefore all Pokemon are based on weapons."
That's more or less the same argument.
Anything can have 1 detail that resembles a specific thing if you are willing to squint hard enough. That's not even getting into the fact that all of the other water starters DON'T have something that resembles a weapon. Greninja doesn't, and Feraligatr doesn't. I know people try to clam "brass knuckles" for the latter to which I have to ask, have they ever SEEN brass knuckles? They don't look like that, at all. The ridges on its arms are an extension of the ridges along the rest of its body. Like it legs and side.
For Greninja, the "theory" (a term I use extremely loosely since theories have evidence backing them up) gets even MORE nonsense as it had to be modified to include attacks too, which ties into what I said at the top. I guess Charizard is based on a weapon as well since it can use Flamethrower, which is an ACTUAL weapon. So is every other fire Pokemon of course. And most electric types are as well since they can use Zap Cannon, and hey a cannon is a weapon. Let's also not forget every Pokemon that can use Swords Dance. A Sword is a weapon, and since Greninja establishes that being able to use a move with a weapon in its name qualifies so is Bidoof.
Hell, Bidoof actually fits BETTER because a sword is an actual weapon, rather than a tool for distraction the way a shuriken was.