"I shouted, 'Anybody here? Get out! Get out! Fire!' " he told the Washington Post, recalling that he was about to leave when he saw a teenager at the top of the stairs, gathered with a group of younger children.
It was 18-year-old Seionna Barrett who was babysitting her three younger siblings and one of their friends while her parents were out playing darts.
The eldest child had run around the house waking up the younger kids after she smelled smoke and Bostic had arrived at just the right time to save then, guiding them through the spreading smoke to the safety of the street.
"He's a real hero, and my daughter's a real hero for waking the kids up. I don't like to think about what might have happened if Nick hadn't shown up. I'm grateful beyond words."
Lafayette Police Department's Lt Randy Sherer echoed that, saying that Bostic's selflessness was inspiring.
"What he doesn't understand is his actions weren't ordinary, they were extraordinary.
"He went down those stairs to save that little girl when he thought it was impossible just moments before ... There's only one way to define that: courageous and heroic."
Bostic suffered burns, smoke inhalation, and a major laceration on his arm and faces a big hospital bill.
Well-wishers rushed to the GoFundMe to offer donations.
"Going to the hospital is expensive ... I'm really grateful that everyone has been so kind and giving," he told the Washington Post.
A few days after the rescue Bostic was able to meet with the Barretts when they invited him to church.
"It was a nervous moment and also tear-jerking," Bostic said. "I was just trying to do what was right that night, and to know they're all okay, I just wanted to cry."
"Nick is far more than a friend to us," David Barrett said. "He's now officially a part of our family."