Wow, ok...
First, yelling "watch out" does not absolve you from responsibility. No matter the disability you have, if you plow into anybody in a legal location, in any vehicle, you are liable.
Second, WDW is private property, anything happens on private property, the property owner can be liable if any negligence can be attributed to the owner.
Third, here is the negligence. Scooters are NOT wheelchairs. Scooters move way too fast for safe travel in large crowds. WDW, imho, is negligent in allowing small heavy fast motor vehicles to whip around their parks. It amazes me that this continues to be allowed. They are dangerous, period! They need speed regulators and idealy some experience to drive before setting them lose in crowds. Think of them as golf carts or little cars and you have a better picture of liability. Again, not wheelchairs.
Fourth, this should have been treated as a vehicular incident in that the police should be called and a report filed. If anyone plows into me or my family and moderate to major injuries occur, I am likely calling the police and if you try to wheel away, I'm following you with PD on the line and will explore pressing charges for leaving the scene of an accident. Attitude plays a huge roll in how this plays out. You run over my stationary (not darting around) daughter and leave her with minor to moderate injuries and are super apologetic, I'll probably blow it off. You act in any way like you are a victim, or worse belligerent, and we are going to have a situation involving the PD.
Finally, they did at least design the wheels on the scooters correctly. They are air filled and large. When one ran over my foot, it was surprisingly no huge deal. If they were hard plastic, somebody would have been sued.