The bag material and the waste inside it are two separate questions.
Even if the film meets a compostability standard, many composting programs do not accept pet waste because of pathogen and contamination concerns. Home composting may also be inappropriate for pet waste unless a properly managed system is used for non-food applications.
That means a consumer could misunderstand "compostable poop bag" as permission to place the filled bag in any compost bin.
A more responsible approach is to focus on verified material content and product performance, then provide a clear instruction such as:
"Dispose of pet waste according to local regulations. Compost only where pet waste is specifically accepted."