Sorry this question is so basic, but I walked into a problem and I'm
trying to help debug.

Does the Squid cache only cache dependent on the requester's IP? For
example, if user A uses Squid as a proxy to reach server B, will the
Squid cache only that result for that user? If a different user comes
in and requests the exact same file, will Squid go retrieve it again
and cache for user C?