Driver appears to enter Roundabout for the first time

Roundabout: a road junction at which traffic moves in one direction around a central island to reach one of the roads converging on it.

Dashcam footage of a couple cars entering a roundabout.

It seems to be the first time in a roundabout for this driver. A collision almost occurred.

A roundabout is not a merry-go-round that stops to let people on.

Which driver do you think would be at fault had there been a collision?