According to Disney's own website:
What Is Rider Switch and How Does It Work?
If Guests in your party can’t or don’t want to board an attraction, you don’t have to miss out!
If a child does not meet the height requirement or a Guest does not wish to board a particular attraction, no problem! With Rider Switch, one adult can wait with the non-rider (or riders) while the rest of the party enjoys the attraction. When the other adult returns, they can supervise the non-riding Guests, and the waiting adult can board the attraction without having to wait in the regular line again!
Rider Switch is available at select attractions at all 4 Walt Disney World Resort theme parks.
While I'm not debating that the CM's may be adhering to a height restriction only rule, I wonder if bringing up the website on a phone if they try to give a guest a hard time about switching with a child who is tall enough but not willing to ride and tactfully pointing out that they're contradicting their own online Guest Services information would make a difference? If they're going to stick to that rule, they need to update their online information, otherwise it isn't fair to guests who may be making plans and fastpass choices based on incorrect information.