That totally depends on where they are accessing the site from. It is quite possible for two different computers to use the same ip address. If they are not on the same network as the Moodle site and are accessing over the Internet but from the same location, chances are that the ip address will be the same. If they are on the same network as the Moodle and accessing the moodle site internally, then the ip address would most likely be different.
However, just because they are on the same computer, does not mean that there was any cheating. One student would have to log out for the other one to log in.
When you are setting up the quiz, you can randomize question and answer order which would stop students sitting next to each other to be able to copy. However, students are pretty ingenious and could easily be taking screenshots and texting each other pictures of the questions or they could just have taken the quiz together at the same time with no supervision.