Rehired Employee- Prior participation in company's 401k

Hello, 

This is the situations: 

• Employee met 401(k) eligibility prior to termination on 2/15/2019
• Employee hired at 6/22/2020
• Without the employee making any affirmative election, system generates a 401(k) contribution on her first paycheck based on the contribution prior to termination. 
• The plan has automatic enrollment ( July 2, 2020- automatic enrollment disclosure sent to employee) 

My questions is as follows:

• Doesn't the employee supposed to affirmatively elect participation again once rehired? 
• If so or not, where in the rules does it state this? 

My limited understanding is that unless the employee is automatically enrolled based on due process of notification, there has to be an affirmative election. Am I wrong? 

If the plan document is silent on the issue it sounds like an administrative procedure policy that should be documented and implemented on a consistent basis.