Note that the clerk changed his story. It's entirely possible that he was lying.
The Stasi said he changed his story. But the reported facts do not establish that.
"Could I have some cigarettes. They are for my mother, waiting in the car"
"I still need to see ID."
"Oh I left it in tha car. Please don;t make be go back in the rain for it "
Perfecly consistant with:
The girl had told him her mother was waiting in the car, the store clerk said.
...
"I always check IDs," he said. "Honestly, I saw her walking in the rain and felt bad for her."