Normally when you buy a static IPv4 address you get a single "1.2.3.4". OP is basically saying they have access to something like "1.2.[0-3].[0-255]". /22 is a fancy way of describing that kind of slice in CIDR notation. So they have 256*4=1024 IP addresses in total.
> Normally when you buy a static IPv4 address you get a single "1.2.3.4"
Is it common to purchase (to own, not "rent" as what you get from cloud platforms) single IP addresses? I thought they were always bought/sold in blocks.
No, in general, the smallest block of IPv6 addresses you can "own" is /24. You have to pay yearly fees to your RIR (Regional Internet Registry) as an ANS (Autonomous system). Think of it as owning land and paying a land tax.