You would need to contact the park and maybe even be there to get a 'for sure' answer, but part of the answer may be where the person's lack of height is.
Some people with dwarfism or short stature are small/short all over and would not fit into the restraints safely.
Other people with dwarfism might have a torso that is more average size and have arms and legs that are shorter than average. People with that type of short stature may fit safely into the restraints even though they will never be 'tall enough' to meet the height requirement to ride the attraction.