To be enantiomers, the structures must have the opposite configuration at all chirality centers.
Isoborneol has 3 chirality centers: the carbon where the OH is located and the two bridgehead carbons in the bicyclic structure. Borneol differs from isoborneol only at the C where the OH is located. When structures have different configurations at at least one chirality center (the carbon with the OH) and have identical configurations at at least one chirality centers (both bridgehead carbons), they are diastereomers. Borneol and Isoborneol are diastereomers.
