It is often overlooked that there were ~2000 years before the flood. Man lived here with angels, nephilim and giants. Look at how far we've come in just the last few hundred years, without any angels, giants, or nephilim..
You left out the most important:
1: sars-cov-2 has never been isolated in a human anywhere, ever. 2: they have no way to test for it. PCR is not a test and none of the tests can distinguish between "covid" and the flu. 3: flu deaths were effectively 0 last year, while covid deaths somehow managed to be approximately what flu deaths should have been. 4: hospitals were paid for "positive" covid diagnoses and treatments.
Most likely some combination of both. We do know there was definitely some tech involving genetic manipulation. Enoch as well as canonized scripture cover what the watchers (angels) taught man how to do.