Iranians may not have needed sophisticated GPS spoofing to bring down the drone, though it might be in their interest to claim such capability.
If the drone did not have an INS as default nav source AND an automatic program to use the INS for navigation to home base in case of loss of other guidance, then all the Iranians had to do was: 1) Track the drone with radar or visually and note when the drone is on a heading toward the center of Iran, 2) Jam the GPS signals so the drone goes stupid on that heading, 3) Jam any other drone control frequencies so the drone cannot be controlled remotely and 4) Continue to track the drone with radar or visually, and pick it up when it runs out of fuel inside Iran.
Any drone you do not want to fall intact into enemy hands should have either an internal INS-return to base program, or a self-destruct program, in case of loss of GPS. The drone in question may have had one or both, and one or both failed. Or it may have had neither. An INS would add weight and cost...
