Adding the inactive users to the channel

Hi ,
I see that there is one inactive user who was earlier present in one of the chat group and was removed later . But for some reason the same user got added to the same chat group after an hour or so .Can we know what might be the reason for him to add in the group back
Want to know how its possible from sendBird javascript SDK as we are not calling any such method addMembers() orJoin() etc
Please help / Suggest