Locked inside car when battery died.

We have a 2016 Rogue and just drove it home after replacing the
transmission. The following day, it wouldn't start.  After jump starting it and
driving it around, I shut it off and realized I was locked inside and I couldn't
unlock the doors.  The car was dead again.   Luckily, a family member was
outside the vehicle and saw me motioning. I removed the keys and at that
point, my family member was able to open the doors from the outside.  (The
key fob battery is new but wouldn't function given the dead state of car.) The
only thing we can identify is that after I removed the mechanical key from the
ignition, he was able to open the doors from the outside.  However, without
him there, I would have still been stuck in the sweltering heat which is a
terrifying thought.  Can anyone help us understand what might have
happened?