A class C means 256 consequetive IPs. Like, A.B.C.4 and A.B.C.200 are both in the same C class. The entire C class usually consists of A.B.C.1 through A.B.C.254 and if two IPs are in that range then they're in the same class C address space.
When google scans the internet it makes a note of the IP address of each URL among other things and if the spiders detect a mininet cloud of 50 interlinking blogs whose IP addresses all coincidentally fall in that that same old C block then google suspects that something is afoot because they're quite likely hosted on the same server.
This is why people go out of their way to rent $5 VPSes from dozens and dozens of different ISPs if they're making these types of blog networks.
You don't need an "SEO host" to do that for you and in fact you SHOULD take care of it yourself because if you purchase 100 IPs from this helpful "SEO host" then guess what? The AS number(autonomous system number) of all or most of those IPs will likely point back to the same webhost. And of course, google will know that something is afoot.
BTW when you rent a VPS you get a dedicated IP, in other words you're the only site with that IP. If you lease a Cpanel account you're sharing that IP with hundreds of sites, some of which might make that IP a "bad neighborhood".