They were moving around slowly or with small movements. Exactly what they were doing depends on who they are, employees, customers, thieves, etc. If they were customers, they could have been just slowly browsing through the goods in the store. A person can also "stir in his sleep." Leaves can "stir in the wind." If someone or something "causes a stir" it means there was reaction or response. The latest Wikileaks release has caused a stir."

They were setting up for the day

stir = the first movement you make from being still He didn't stir = he did not cease being absolutely still When corpses stir, then you should run!