According to the report, it seems that TSMC’s 10nm manufacturing process is what won them the exclusive rights to build the component. TSMC is also rumored to use more advanced device packaging techniques that apparently improves the chipset’s performance and efficiency, hence leading to them being chosen.
Prior to this, both Samsung and TSMC worked on the iPhone 6s/6s Plus’ A9 chipset. There was also a bit of controversy regarding the chipsets as not only did the Samsung and TSMC-made A9 chipsets come in different sizes, but it was reported that the TSMC-made A9 had longer battery life.
Of course these results are based on lab testing and obviously real-world results are what truly matters, but either way we will probably have to wait and see if the rumors are true upon the teardown of the iPhone 7/7 Plus later this year. Until then, take it with a grain of salt.