but the government has drones
Boots on the ground. Try to control a subcontinent of 325M people with drones and planes, when every corner could have an armed citizen. Ask the vietcong, or the afghani, how much they could do with small firearms.
"Where the people fear the government you have tyranny. Where the government fears the people you have liberty."
edit: grammar
By the way, the article does its own share of data-wrangling by happily omitting the kinds of guns people own and how. In US one can simply buy an assault rifle. Down in Europe you need training, screening and physical exams of your home to get a gun. Both count as “a gun owned”
So because something it's unlikely to happen you shouldn't take steps to protect you against it? Why having insurance, for instance?
I think the example isn't instructive as to the importance of widespread ownership. If there is a large group that wants to raise hell for a government, they will be able to obtain weapons.