security - Linux File Permissions & Access Control Query

Let's say I am user bob in group users. There's this file:

-rw----r--  1 root users     4 May  8 22:34 testfile

First question:
Why can't bob read the file as it's readable by others? Is it simply that if you are denied by group, then you are auto-blacklisted for others? I always assumed that the final 3 bits too precedence over user/group permission bits, guess I was wrong...

Second question:
How is this implemented? I suppose it's linked to the first query, but how does this work in relation to Access Control, is it related to how ACLs work / are queried? Just trying to understand how these 9 permission bits are actually implemented/used in Linux.

Thanks alot.