It might be propaganda.
But there is neither effective health care nor health surveillance, nor functioning labs, in ISIS controlled areas. It would be impossible to confirm a case, but that does not mean that the disease is not present. Any traveller could have taken it there, just as it has been taken to other a few other locations beyond the main affected countries during this outbreak.
If (and that's a big if) it is present there, there may be a cluster outbreak and it would become noticed at some point. Travel in and out of ISIS-controlled areas is already limited (and dangerous). I doubt even military medics could be deployed to assist there safely, and no volunteers should be permitted to go.