Not op so not sure. But i think the logic here is sharing your idea with a powerhouse vc may get that idea leaked to their network and particularly, someone that can execute on it.
I think every investor ever will tell you ideas are worth 0 without execution. No entrepreneur I am aware of will keep their ideas secret. You will have to sign an NDA if you're trying to dig deeply into their solution which is the more valuable piece.
I won’t lie. I saw a16z and somehow just translated that as “Amazon,” despite knowing exactly who they are (and having pitched to them–not personally–at a previous startup).