An adult, non parent, had set up a bottom rope for a teen, the teen top roped it twice. then went to clean the anchor.
at the anchor the teen connected a quickdraw on to the lower off untied the rope and tied it to another draw on his harness.

I was on a near by route with a clear view, seeingthe confusion on the teenagers face I waited on a hold for a few moments.

his belayer had LOADS of slack out and no hands on the rope, just leaning against a tree with arms folded. shouting up something unclear.
The teen only connected by a a quickdraw to his harness started trying to unclip this only point...

this is when I shouted over what to do, in order to prevent things getting worse

the climber returned to the ground safety went and left shortly after.