It isn't compatible with Falcon, it can be made to be compatible with Falcon in the future. It wouldn't really be worth doing though, since part of the point of

It isn't compatible with Falcon, it can be made to be compatible with Falcon in the future. It wouldn't really be worth doing though, since part of the point of having two providers is dissimilar redundancy, so that any issues with one platform don't affect the other. It's more likely that if Boeing wants to keep flying Starliner after using up the stock of Atlas Vs, they'll want to integrate it on Vulcan Centaur rather than Falcon.