If paget's breast cancer spreads to the bones, then does that person have paget's bone disease?

No: Despite similarity in names, Paget disease of the bone is very different from metastatic breast cancer. Paget disease of the bone is generally localized bone malformation, though is may cause bony deformity, fracture, pain and in rare cases lead to bone cancer.

Two different things: Paget's disease of the breast is a particular type of breast cancer that starts under the nipple. Most are very treatable, but like any other breast cancer - advanced cases may metastasize. Paget's disease of the bone is a chronic problem that is not realted to cancer.