Both sides have every reason to lie and make the claims they are making. Admitting Iran did bring the drone down would be embarrassing for the USA, so of course Iran is going to assert they brought it down and the USA is going to assert Iran just got lucky when the drone came down due to a malfunction.
Regarding the latter claim, it’s interesting to note that the assertion US drones are often programmed to land if they lose communications is a statement consistent with both sides’ claims. It obviously lends credence to the US claim, as it explains why Iran was able to retrieve the drone intact as opposed to scoring only a few bits of charred debris.
It also lends credence to Iran’s claim. First, any communications for controlling the drone would obviously be very securely encrypted. Managing to crack such encryption in real time is highly unlikely. That leaves Iran with the option of simply jamming the control signal, by using high-powered transmitters to overwhelm it. If a drone is programmed to land when it loses contact, then jamming its communications link is effectively sending it a command to land. Note, however, that such jamming is hardly (as Iran claims) “sophisticated;” to the contrary, it is rather crude and brute force measure.
The only truly sophisticated technology Iran needs is a radar system capable of circumventing whatever anti-radar measures US drones typically have, so that such drones can be detected and intercepted. Interestingly, Iran claimed to have acquired precisely that capability last October.
At this point, however, it’s strictly a “he said, she said” story. What would definitively lend credibility to Iran’s claims is for a second drone to be captured by them in say the next six months. Such a feat would be more than can be explained simply by getting lucky.