Ideally, for redundancy, you'd run in more than one datacenter. That's hard to do with only one /24; most networks won't take BGP advertisements more specific than /24, so you can't easily run half your ips at each DC. Maybe HE allows it for transit customers, but it makes the routing messier.

They could be doing anycast, but that's pretty sophisticated. They could also only advertise the /24 from one DC at a time, but that's error prone. Or maybe advertise from both and forward to the live DC over a private link/VPN.

I do see in Octoberish, they were peering with a second network, and they have second network in their IRR records. Could just be so they can use one of the DDoS filter companies that advertises your netblock, and sends you clean traffic. Can't do that (easily) if you get IPs from your transit provider and it's not a service they support.