Riddle Help

2. My friend Bob went back to his hometown for Thanksgiving last year and while he was at his parents house sleeping on the couch, an old high school friend stopped by to visit.
"Hey Bob, good to see you. Boy I bet it's been almost twenty years."
"You look great," Bob said. "Tell me what have you been doing? I hear you've been running your father's gas station?"
"Yeah, but more important than that, I'm married. In fact, I married someone who was a year behind us in high school and I'm pretty sure you didn't know. By the way, this is my daughter," the friend said.
Bob looked down at the little girl who was five or six years old and extended his hand and asked the little girl her name.
"My mother and I have the same name," she said.
"Oh that's nice," said Bob. "Then I guess your name must be Annie."
How did he know?