IMO they are both crap drivers and both at fault here, I would argue that the biker is more responsible for causing the collision but both are guilty of poor driving.
The car was leaving the roundabout but changed their mind and turned sharply to carry on around without looking - bad.
The biker was also leaving the roundabout from the same lane but attempted to accelerate around the car in front so he could squeeze between them and the central reservation to get ahead - bad.
The car made a mistake by not looking, however the biker should not have been there so both are at fault and both were driving without due care or attention, but more so the biker IMO as his was a deliberate act.
The car was leaving the roundabout but changed their mind and turned sharply to carry on around without looking - bad.
The biker was also leaving the roundabout from the same lane but attempted to accelerate around the car in front so he could squeeze between them and the central reservation to get ahead - bad.
The car made a mistake by not looking, however the biker should not have been there so both are at fault and both were driving without due care or attention, but more so the biker IMO as his was a deliberate act.