Here's how it went down. Sojiro was a government official that acted as a liason between the establishment and Wakaba Isshiki's research lab. It was implied that he often made coffee and curry for Wakaba because she often didn't take good care of herself due to having to raise a child as a single mom alongside her job as the lead researcher of cognitive psiscience. She then refined these recipes which gave rise to LeBlanc's signature Coffee and Curry combo.
After Wakaba's apparant suicide, which hasn't happened yet, and taking custody of Futaba, Sojiro left his job at the government and became the owner of LeBlanc in order to protect her from her mother's enemies.