Why would a revised manuscript following very minor revisions appear as "under review" in the journal management system?
It is not uncommon after minor revisions that the paper is indeed send back to (usually the same) reviewers. In most cases another round of revisions is not needed and they will simply accept the paper, but this is of course not guaranteed. 

For some journals, as a reviewer, you can indicate whether you want to see the paper again after minor revisions, I do not know whether this is an option for Elsevier journals.