Just perhaps the older gentleman was trying to enforce his version of the law like some on here try do frequently, also the footway may well have been a shared use path in which case the older gentleman may well be in the wrong.
As a parent if you find the roads to dangerous for your children to cycle on, what are you doing about it, organising petitions, phoning police and local councillors about your concerns, and copying in the local media, and council cycling officer.
Then there is also the reason of you that should be asked if you believe the roads are dangerous and you tell your son to use the footway, that may not be shared use,why is he out cycling on his own, obviously untrained and supervised.
Roads as an entity are not usuually dangerous, its other road users who make roads dangerous, and perghaps your anger should be aimed at those people who fail to use the roads and footways with respect for other users safety.