It says it's off. You're a journalist reporting against a fascist regime. You, your family, and known associates will be tortured and killed if you are found. Do you trust it, or a mesh wire lined bag that physics says definitely will block it?
Realistically, if your adversaries are capable of communicating with your phone while it's turned off or in airplane mode, your best solution is probably just to hit your phone with a five dollar wrench until it breaks.