I'm sorry, but no, he is not even one iota correct, except by the most abstract approach to viewing the world. One does not just get to play semantic equivocation with definitions for no reason. This is why I asked snidely if he was a plant. As a plant, CarbonDioxide is your fuel, and Oxygen is your waste product. However, unless some things have changed, most plants do not get on the internet and make stupid little posts about coal power and post pretty and inane pictures. We are humans, and we view things from an anthrocentric perspective, and that is how we define things.
Humans are perfectly capable of taking other views, for a example a more general view, like that of "earth". With such a perspective "waste" would certainly mean something different (the definition might be the same: maybe "something of no use to
someone". So for a human, CO2 can be "waste", for the earth it certainly isn't. The "waste" of earth might be the radiation it is dissipating or the odd piece of man-made machinery that manages to leave its orbit.
Of course we are capable, but we do not do so on an every day basis, so as to undermine the foundations of our basic communications. If we had to rewrite the definition of the words we used every time we had a conversation in order to accept every and all viewpoints everyone brought to the table, communication would be literally impossible (or at least improbable/burdensome).
Excepting specific case-by-case basis where there is a NEED to use common terminology in an unaccepted way, to make useful conversation we are constrained, this is why we agree to use certain words in specific ways. In the case of this thread the concept of redefining waste because it does not apply to plants is stupid and only done to serve the purpose of those who are either trolling, or for some reason seriously believe dumping toxic (to humans I now have to define) gases in unlimited quantities into our atmosphere is at worst a neutral event, and feel that "waste" is a negative propaganda term.
I still question why you would defend this viewpoint. As you mentioned yourself earlier, by viewing "waste" either as "something which is not useful to someone", or as "something which not useful to anyone", you make the word worthless, as it now applies to everything, or nothing, respectively.