By saying that Character A breathed/blinked, the character did something. Thus, because words are written, the idea exists, thus it has substance. In this sense, it is substantial. In an informal sense, substantial can mean "in a large amount, size or number," or "ample to satisfy or nourish," to inadequately fit the context of where you used it, but I was adhering to the strict derived definition of the word, "consisting of or relating to substance" in order to be sarcastic and (hopefully) witty. 

You are confusing meaning with existence. Had you substituted, "meaningful" for every "substantial" in your previous post, it would have been sound logic (albeit stating the obvious). It would be easy for a creative or imaginative person to find meaning behind actions like breathing or blinking outside of any context, but that's not the point. 

The point is that I was sarcastically trying to encourage you to make your post so we could keep rolling along with the RP, not to entice you into a logic duel of wit and banter.