On an average, peer review takes anywhere between 1-3 months. It is rather unusual for the review process to be completed within a week. However, journals using ScholarOne Manuscripts often have a shorter peer review time. As mentioned in the IEEE website: “Electronic submission through IEEE ScholarOne Manuscripts speeds up the review process and shortens the time between manuscript submission and publication.”
You should check the website of the journal to find out the average review time. It is possible that the journal has a shorter review time: some journals provide a shorter deadline to reviewers to speed up the review process. Another possibility is that the journal has a rapid publication option, in which case it is quite normal for the review to be completed in a week’s time.
It is difficult to predict whether a short review time indicates rejection. I don't think there is any clear correlation between the time taken for review and its outcome. If a reviewer is quick, or is not tied up with other commitments at the time, it is possible to complete a review within a week's time. Additionally, ScholarOne also provides some facilities, such as click-through citation linking, which makes the peer-review smoother and less time consuming for reviewers.