Talent selection exists to make the most of athletes already inside a sport's talent pool: rather than training every participant identically, objective testing separates out those most likely to reach elite level and channels extra coaching and resources toward them.
Talent transfer exists to solve a different problem, a sport short of world-class athletes can borrow ready-made physical qualities from athletes already excelling elsewhere, cutting years off the development timeline compared to training a complete beginner.
The core distinction is therefore about direction: selection operates inside one sport's pipeline, sorting current participants by potential, while transfer operates across sports, moving an athlete's already-developed skillset into a new discipline where it fits even better.