It's an infationary use of "illusory". "Social constructs" describe certain regularities in the real world, maybe not very useful regularities often presented in a confusing manner, but something real nonetheless. "Illusory" usually refers to a falsity, so its use in this case doesn't seem appropriate. Furthermore, being a bad fit, this word shouldn't be used in explaining/clarifying your actual point, otherwise you risk its connotations leaking in where they don't follow from your argument.