I’d say that’s a smart deal.

Ipv6 will bring more addresses once / if it’s finally widely adopted

To answer your question, IP addresses are what computers use to identify and talk to each other. You get assigned a temporary one by your ISP through your modem, but they still own the actual address. Similarly, many businesses own their own blocks of IP addresses, so anything in that block will route to them. In this case Milwaukee had a block of addresses they didn’t need and are selling them to an ISP.