I think this is a bit disingenuous and intentionally sensationalist, nobody has any reason to believe that the Assistant is always listening or will just trigger randomly or on demand by Google because they want to listen to particular conversations, that doesn't even really make any sense. Also various parties have access to the source code, so if it were malicious, there can be evidence of it. That there isn't any evidence is important to mention in this context.
In reality its just that it can randomly miss-classify "Ok Google", nothing malicious about that, and obviously the purpose of the annotator is to look at unrecognized samples, so obviously they are gonna frequently hear those cases, that's sort of the whole point of this.
Maybe "well, duh, how do you think it knows your voice? magical pixie dust?" is a bit of a cop out, but honestly there are two options, them doing what they are doing right now, and not have Google Assistant.