There is always a trick for everything. Just gotta figure it out.
I'm not surprised by the amount of users he follows per day, rather than the delay he has between each one. I think that's pretty much impossible. Do you have some proof to back your words?
He could be using some type of exploit to bypass API limits. I remember someone in the forum being able to do this and follow 2k-3k people in one day.
I follow 2k people a day
Delay follow 30 to 30
So I get at least 550 a day to follow back
Being doing this for 3 weeks am not sure
Everything is OK no ban
But the dude your taking about
What he's doing its not safe to use 1 sec delay
He will get ban soon .