I could not find anything about how or why this name change occurred.

Oei Ek Tjong (1921?-?)

He was born to a trader from Sulawesi and he was originally from Quanzhou, China. He would join his father in setting up shop in Makassar. Widjaja would leave school to work as a hawker and sold cookie and candy from his bicycle. Prior to the Japanese invasion of Indonesia, he would go on to work several odd jobs.

Eka Tjipta Widjaja (?-2019)

Widjaja: (Indonesian) victory; derived from the Sanskrit word vijaya

Widjaja would become one of the wealthiest men in Indonesia.

Sources