How did my friend get so many followers on Twitter?

[John Sin]

Hey everyone, so last week my friend had probably about 80 followers on Twitter, but then one day it spiked up to 100. It didnt really mean much to us until the next day it was at 500 and by the end of it all, it stopped at 1013 followers. I think it's like a virus or something because most of the accounts tweeted the exact same things when i checked, and i was just wondering if anyone knows how this happens so i and whoever reading this can do it too
My friend never followed anyone, and remained at 80 following as his followers increased lol