In the article they talk about getting hit by millions of different IPs. It's probably on a different level compared to what a random, non-targeted site has to deal with.

A few years back when graphics cards were getting botted for resale, a friend of a friend was buying with bots using a (pricey) rotating list of hundreds of proxy addresses that would each make attempts at a very reasonable looking frequency. I'm picturing something like that, except with much more funding.