It appears his ASN has quite a few naughty spammers withen. And it looks like these poor people have had their routers busted open by a hacker to turn it into a zombie bot through port 2000.
https://stopforumspam.com/asn/26077 Click on abuse history.
https://www.speedguide.net/port.php?port=2000
I interacted with Lumpy through PMs and I checked his IP out with several websites and his router hasn't been turned into a zombie botnet. So the premise that Spamhaus uses subnets, CIDRs or ASNs may ring true based on Stop Forum Spam's data on this ASN belonging to his ISP.
Edit-
It would be prudent for this website to instead use the Stop Forum Spam API instead of relying on Spamhaus. Waaaay more effective and I use it myself. After all, it's free.