Perhaps it was swamp gas.The big-shots in the government said it was only swamp gas and downed played the whole thing.
It's easy to become panicked by something that is difficult to explain. I remember driving home one night along dark country lanes and seeing strange lights in the sky reflected in my rear-view mirror. I was quite spooked by it as they seemed to be following me. From the safety of my garden I took a closer look with a pair of binoculars - it was a laser display by the local rugby club.I've talked to people who remembered that day, and they thought it was the END of the WORLD!
The thing is what is more likely? Marsh gas, laser display or aliens locating the Earth from across the galaxy, travelling here and whilst hiding most of the time, sometimes make the mistake of letting us see them?
In every other walk of life, humans live their life on the basis of probability - they cross the road within 30 yards of a bend in the road because the probability is that there isn't an F1 racing car being tested at 200mph on that stretch that will undoubtedly kill them before they can get to the other side.
We eat processed food every day on the probability that it hasn't been poisoned by a mass murderer at the food plant.
I could go on. But the point is that rational human beings, who make every day decisions about their lives on the basis of probability, suddenly suspend this rationality when they see something they can't explain - but would like to explain by something that they long to come true.
It's more likely that someone is going to be run down by an F1 racing car outside their house than it is that they are going to see an alien spacecraft (especially when they're obviously trying to stay hidden).