It's answered in the article. The argument is not that giant creatures can't exist, but that they cannot exist as a simple scaled-up version of the otherwise identical smaller version.

i can’t read the article to see what the specifics are, but assuming it’s essentially the square-cube law it doesn’t mean giant creatures can’t exist, it’s that small creatures can’t scale to be giants while being unchanged.

again i’m guessing, but if the conclusion is something like “if giant humans existed, X, Y and Z wouldn’t work”. then a “giant humans” would have to be something decidedly non-human.