From their About us page:
"We’re the Regional Internet Registry for Europe, the Middle East and parts of Central Asia. As such, we allocate and register blocks of Internet number resources to Internet service providers (ISPs) and other organisations."
This interface is the historical bgp announcements for this particular ASN. The X access is time. The Y axis is ip address blocks.
So some employee at an ISP registered IP addresses over time in such a way as to create this pattern? Kind of like how people make art out of their github commits [1] (only without the ability to retroactively modify the dates)?
Nearly, but they didn't register them, they just had their network announce routes for them (which is just telling other networks "hi, if you have traffic for this IP range I can send it on", the registration is unrelated to that)