You have not mentioned whether there were any other statuses before "Under review." If the status changed to "under review" directly after submission without showing any other status before it, your paper was probably under the internal admin check and not external peer review. The status "Editor Assigned" typically indicates that an Associate Editor (AE) has been assigned for your paper. The AE is responsible for processing your paper from initial editorial screening to the final decision. It is the AE's responsibility to send your paper for peer review. Since the AE has just been assigned, it is clear that the paper has not yet been sent for peer review.
I think that for this journal, the status "under review" is used for both internal and external review. So basically, your paper has cleared the admin check and has just been assigned to an AE. The AE will conduct the initial editorial screening to check the scientific value and relevance of the manuscript to the journal. Your paper will be sent for peer review only once it clears this screening.
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