Electron configuration of transition metals sometimes get complicated due to some "irregularities". If you have NEVER noticed this, look them up in an inorganic textbook. This paper doesn't really give you anything new if you already know the underlying reason for those configurations. However, the authors did a computational experiment to show us which orbitals are more stable upon adding an electron. So, that's useful in terms of teaching.
The summary is that "there is no scientific reason to write the electron configuration of transition elements as [Ar] 4s 3d and the correct form is [Ar] 3d 4s."