Rear door locked, couldn't open

When I parked my car today my son couldn't open the back right side rear door today. I couldn't even open it from the outside. I opened the left rear door and I seen the child locks. I pushed it up and down to see what it would do the other door and it worked because I could open the door on the outside. Somehow the child lock was pushed to lock mode on his door, but why couldn't I open the door from the outside originally?

 

I tried that too and I can still open his door on the outside. My son did tell me that he manually unlocked the door while I was at a slow rolling stop going 2mph in our driveway.

 

I hope so, I will have to keep an eye on that because that freaked me out.