I've been on mod teams with him and some other powermods. They don't do shit, just have new mods do all the work as they and their friends set up 'org charts' according to which they run their subs.
That is an objectively sad life. Imagine people asking what you did with your life and your answer is "I had imaginary power on a now-defunct internet site doing unpaid work day in and day out. I spent hours upon hours of my life creating charts that only apply in this digital universe to make myself feel important while people who scrolled my page for five minutes a day on the subway were out doing things in the real world".
That would still be an enormous task for a single person. Let's pretend they really only had to deal with not more than a single post from each sub every week:
1,000 comments/posts per week = ca. 142 per day. If that mod takes as little as two minutes to read and properly reply to each of those, that would amount to a daily 4-5 hours of unpaid work in their spare time.
Turtle was active on Reddit about 16 HOURS a day so it was certainly possible. Of course they didn't actually do much of anything in those subs, they just collected them.