Ah, well then. I've never used an ISP that leased a subset of addresses within a CIDR -- in your case, what appears to be a 13 address range within a /24.
I wonder what isolation method is deployed between customers on the same subnet. One would hope they have one. But perhaps all they're doing is blocking broadcasts. Perhaps.
It's my guess that this gives them addressing flexibility as customers come and go. IPv4 is fully committed.
Do they also offer IPv6? If so, addressing schemas may be normal -- if anything in IPv6 can be described with that word.