They aren't saying they think that's the price, just that this is what they are guaranteed to pay by December.The $8.61B number is wishful thinking on Disney's part.
Key part of the Press Release
"Under the appraisal process agreed to by Disney and Comcast, Hulu’s equity fair value will be assessed as of September 30, 2023, and if the value is ultimately determined to be greater than the guaranteed floor value, Disney will pay NBCU its percentage of the difference between the equity fair value and the guaranteed floor value. While the timing of the appraisal process is uncertain, we anticipate it should be completed during the 2024 calendar year."
I can imagine some people in Philadelphia are laughing right now.