That is true.
The reasons are that the attraction changes from being on the ground for boarding and unloading to being suspended in the air during the ride. They can't have people inside the attraction hanging there above the ground while it would be stopped for someone to board.
The moving walkway is also fairly short, so gives much less time to get on than some others.
Theses are the reasons why WDW lists it as an attraction where guests must be ambulatory.
This is what I wrote about it in the disABILITIES FAQs thread in a post on page 2 about attractions with moving walkways:
Peter Pan - can only be stopped in emergency, and stopping requires an evacuation of the attraction.
Sometimes, it is possible to have the CMs stop this attraction for the very first or very last ride of the day. Because of how this ride operates, they can only stop it for boarding if there are no other guests on the ride. For the first ride of the day, they would load guests with disabilities with only a small number of other guests on the attraction (the number who would fit in the cars on the stopped walkway) before starting the walkway. At the end of the ride, they would stop the ride and all guests get out before re-starting the moving walkway. (This information is from an area supervisor at MK).
You can find the disABILITIES FAQs thread near the top of this board or follow the link in my signature.
Also to be aware of - the getting on might be OK, but guests must be very quick to get off. The last time we've ridden, our daughter was small enough to carry on. My husband did not have a lot if trouble getting on with her, but nearly ended up running out of room getting off.
So, you may want to watch loading and unloading for a while before deciding whether you can manage it.