I was forced to read this in freshman English… it was awful. Realized you could make it say whatever you want and used that for the essay I wrote
That's a non-sequitur. What they are saying is that: "if a text can mean anything, then by definition it means nothing."
Not coincidentally, this nothingness is part of the postmodernist project of "destabilizing meaning" which is in direct opposition to, as a rejection of, the progress of technology and science, which instead seeks to discover empirically what things are and what the truth is.