Before wdw could open or any business for that matter, they had to submit a plan that the governor had to approve before they could reopen. Once this specific plan was approved by the governor, wdw had to follow this plan as if it were official law and if they did not follow the plan they would be forced to shutdown. If u do some research u will find that part of wdw plan to open was:
"Disney will be temporarily suspending parades, fireworks, and shows that “create crowds.”
Whether wdw wrote it or not is irrelevant, it is still part of their approved plan by the governor and they have to follow those restrictions or risk being fined or shut down. Once that plan was approved and signed by governor, it became restrictions that will be enforced by the state or county. Just because it says temporary doesn't mean they can just start back up at their own discretion, the state controls the different phases for opening up. Just because seaworld can do fireworks doesn't mean wdw can, if seaworld didn't list suspending fireworks as part of their plan then they can continue to do fireworks.