This scenario is possible only if a lead interacted with your scheduler again, but dropped off on first step, and didn't book a call.
Quick reminder before we proceed. The beauty of iClosed that it catches all leads from your scheduler, no matter the stage in the scheduler, which helps you gather data about all leads and gives you opportunity to reach out to them and convert them eventually.
We've reproduced this case and here's step by step guide how this can happen, with a video walkthrough below. This scenario is possible only if a lead used same email address or phone number (depending on which of the two is set as primary invitee question).
Lead scheduled a Strategy call
But, lead visited scheduler again after certain period of time
Lead entered same phone number or email he used for scheduling a call previously
But, realized he scheduled a call already, so he dropped off (closed the page)
iClosed caught this lead as potential, but since the phone number/email data was already collected, we didn't create new potential lead, but recognized existing and updated it's status.
To change the status back, navigate to leads contact card
(accessible from 
Global Data → all sections or 
AI Scheduler → Scheduled calls)
Click on Status on the left, and select correct status. In case status is tied to calls, you'll be asked to schedule a call, but in this case, choose "Add later" option, that will just change the status, without booking a new call.