Nothing to support that medical conclusion. They are drawing a inference that likely cannot be supported by available data. Yes, child lived. Seizure generally requires little advanced medical care, and in almost all situations immediate care is all about the airway. Oxygen is nice, but generally not critical. What is critical is maintaining a patent airway continuously. This can be done in an unsecured patient, without a stretcher, bouncing down the road; but likely not well.
Well meaning heroics by the volunteers, and the patient did well despite their efforts.
But this is not an example of overlawyered situation, and review of policy and basic first aid for them is probably a good thing.

n.b. my basic kit in the trunk of my car contains a mask/breathing bag, supraglotic airway tools, and stuff to stop bleeding. I would not venture to scoop and run with a seizing patient if a full complement of resuscitation (ambulance) were on its way.