If this drone was flown by the army then..and sorry army bro's, the IFF probably wasn't on or had did not have its codes loaded. On more than one occasion in multiple foreign locations I offered to load the IFF codes for Army birds after hitting up our USAF ones, and was often told "we never use those".
For those that dont know IFF (interrogate friend or foe) relies on a set of daily codes used by the armed forces that encrypts the interrogation signals. You paint the target with a radar/beacon, ask for a reply, and depending on what you get back identify as friend or foe. Thats the general gist. Its another segment of a regular aircraft transponder that almost all aircraft have to identify themselves to air traffic control.