Good question. My understanding is that impurities can create behaviors in materials which mimic some superconducting indicators such as levitation and sharp resistance drops, but without key indicators such as zero resistance and Josephson effects.

Notably, the original paper only showed behaviors that indicate, but doesn't prove, superconductivity. Several pure samples have been found to not exhibit those behaviors, so consensus is that it's a case of impurities mimicking superconducting behavior.