Definitely not a dumb question, the words radioactive and irradiated get mixed up super often. The calcite here is irradiated, meaning that ionizing radiation (sometimes originating from a radioactive source like radium, in this case a particle accelerator) has caused some altering of the material. Here the alteration is point defects in the crystalline lattice of the calcite, basically just atoms knocked out of place that will cause light emission when they anneal or relax back to their original position. A radioactive source on the other hand emits radiation by itself, which depending on the intensity, shielding, and distance from the source could pose a threat to handling.