Using the numbers for the January 1, 2019 Mega Millions prize of $425 million:
Rounded off. 48 million tickets were sold. You would have to buy 480,000 tickets to have a 1 percent chance, or .01. 48,000 to have a .001 chance. 4,800 to have a .0001.
Buying 1,000 tickets gives you a .000021 chance. Buying just one ticket puts three more zeroes in front of that, .000000021.
Yes, the odds are technically a thousand times smaller, but in the real world, the odds for both are so statistically tiny that there isn't much real difference, and that's what people mean.