Many soldiers have security clearances based on MOS or job performance requirements. The security clearance is granted only after a lengthy background investigation is performed by qualified persons. Your security clearance investigation may have been initiated before you even entered active duty.
Depending on the duration of the investigation, it may have even been resolved while you were in the delayed entry program. You might be thinking you dodged a bullet after having your clearance granted. You may have had several issues in your past that had to be addressed prior to the clearance granted.