Was Sai Baba the only holy person in Shirdi when he returned with Chand Patil's wedding party?

No, Shirdi was already a spiritually significant place with other saints residing there before Sai Baba's return. Chapter 5 of the Shri Sai Satcharitra explicitly mentions that before Baba came back with the wedding party, other holy figures had made Shirdi their home. The text specifically names Devidas, who had established himself in Shirdi, and Janakidas Gosavi, who also came to live there. This context suggests that Baba was joining a community that already had a notable spiritual presence, rather than arriving in a place devoid of other saints.