Many inexperienced cyclists who are accustomed to cycling only on pavements, or in such paltry 'infrastructure' as may be provided, are at a loss when they get to a roundabout and such infrastructure disappears. They are then at most danger. Having said that, this particular cyclist was foolhardy to come off the pavement into the roadway even if indications by motorists were unclear. If you do something which the motorist doesn't expect, prepare to get hit. I don't think your father did anything wrong.
I know of one horrible bit of 'in-farce-structure' and R/B combined (not the same R/B as I mentioned earlier) which I often traverse: this one's on the main junction off the
A23 at Hickstead. You can see the legitimate (and useful) cycle path - downgraded minor road - coming in from the east(just north of the A2300): I often use it, but cyclists are directed by signage first to cross the 'blind' exit to the north, then to mount the pavement and,
going the wrong way round the roundabout, to cross the slip road coming from the southbound A23 to the northwest, then continue on the pavement to the west.
Motorists on this slip road will of course be looking to their right, not to their left, as they approach the roundabout. Incredibly dangerous: I do use the cycle path before the roundabout, but I don't follow the signage, I turn left and go round the roundabout in the normal way. Perhaps something ought to be done about this menace.