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.

In condensed matter physics, impurities refers to impurities in the lattice structure of the material, usually due to trace amounts of other elements or even faults in the crystal structure.