I would not believe that because it says the paper was published 4 days after submission that the review process took that long. Since time to publication became something that journals advertise, they have been using all kinds of dirty tricks to mislead readers about this statistic. For example, where it used to be common after review to send back a "revise & resubmit" response, they started doing "reject & resubmit". In other words, "we are rejecting this submission, but we encourage you to take the reviewers' comments and submit again anew". That way they can count the re-submission as a new submission and their time from submission to publication is shorter since it is measured from the time of re-submission. It's an intentional obfuscation of the actual time it takes to publish something.