I get really aggravated when people talk about "infecting the network." Typically, there are two separate issues in play here. Just because a computer shares a subnet with another doesn't make it vulnerable (or, at least, it shouldn't, barring bugs).
The real vulnerability is in the credentials the infected computer has. On domain-joined Windows computers, the Active Directory service that handles authentication and distribution of credentials frequently is run on (and only works on) a particular network segment, leading to the common misconception that "the network" is not just a means of transmitting data, but a "trusted" thing.
In short, look for what machines the infected computer had access to. If the infected computer was a domain-joined Windows machine, the infected machine and the users logged into it may very well have had access to other computers on the network, placing them at risk. If it was a Windows machine that was not domain-joined, worry about other machines on the network that used the same user name and password as a user on the infected machine, or that the infected machine had saved credentials for (check the Credential Manager on the logged-in accounts).
It's also worth noting that most ransomware isn't that smart. It's not typically a self-spreading thing, just a payload delivered by some other exploit mechanism. It wouldn't really help it to encrypt files on other computers unless it can also display a ransom demand, and that requires code execution, not just file access. Most ransomware won't touch the network unless you have a network drive mapped, and then only because it confuses those with local drives.