I think the term UFO is used somewhat liberally here. Whatever hit the falcon 9 clearly was chemically propelled like a missile. I’d hazard a guess that it was a missile. Given that this was taking classified cargo up to the ISS, and NASA still does not want to be straight with the public about what this cargo was, my guess is some foreign power that did know and was able to get a missile launcher in place in advance, took it down to prevent delivery. That foreign power being terrestrial in nature as no extra-terrestrials could possibly get here from another star system under chemical propulsion.