Human speech is not mathematical formalism. What would even "open-source" mean in case of hardware, is there a consensus on it to begin with? Is it only 'every firmware is open-source and available', or would you want the whole floorplan of the chip?

So given that the word doesn't really apply to hardware, I believe they used it correctly (100% means the set of things where it makes sense to be used) and are not misleading. In fact I strongly dislike some of the "open-hardware" marketing of some previously mentioned devices, when that is obviously false and misleading.