The article said radioactive materials can become concentrated by activities "like" fracking. Some people think in situ leach mining--in which lixivants are injected in conjunction with oxidants to bring up metals like uranium or copper--is "like" fracking, and in situ recovery mining of uranium does indeed concentrate uranium. Fracking would probably not be an effective mobilizer of uranium, but chemically, it could be a mobilizer for radium--which has a lot of chemical characteristics in common with calcium.
Fracking may bring up radioactive material from depth but if this material is the same as the bedrock at the surface, how does this "concentrate" radioactive material?
By chemical reaction, fracking fluids can selectively liberate certain elements or compounds from the groundmass, Then concentration could potentially occur at the surface where the return fluid is filtered, partly recycled, and sometimes put into evaporation ponds--activities which are all routinely part of the fracking process. Radium would be of particular concern because it has several water-soluble forms and decays to radon gas, making both mobile, and potentially ingestible (radium accumulates in bones like calcium) and both undergo alpha decay with accompanying gamma emissions. Different locations, different rock formations, and different fracking fluid formulas would have varying potential for radium extraction, but it's something which should be tested for and monitored.