Yes, this is right. A better way of saying it might be: "Phlogiston", as ancient chemists understood it, meant "that which makes stuff burn". So saying "Phlogiston causes fire" is like saying "The stuff that makes things burn causes stuff to burn." If you look at the second statement, phlogiston obviously doesn't mean anything.

If you wanted to test the hypothesis "phlogiston causes stuff to burn" you really couldn't, because phlogiston isn't a proper explanation - there aren't any conditions that would disprove it. If you want to even consider the hypothesis in the first place it has to make better predictions than other hypotheses.