Although this girl went to the same school in Chibok, she was abducted in a separate incident, Femi Adesina said.
The 15-year-old girl was found by government troops while she was escaping.
Boko Haram has captured thousands of people in north-eastern Nigeria.
The abduction of the 276 Chibok girls is the most high-profile case but many others have never had any media attention or support, aid organisations say.
Three years since the abduction, 113 Chibok girls remain in captivity.
A total of 103 of the girls have been released so far, including 82 earlier this month in a prisoner swap.
The 82 girls, who met Nigerian President Muhammadu Buhari on 7 May, are expected to be reunited with their families later this week.
They are believed to have been swapped for five Boko Haram commanders.
Last month, President Buhari said the government remained "in constant touch through negotiations, through local intelligence, to secure the release of the remaining girls and other abducted persons unharmed".
Aside from the Chibok girls, Boko Haram has kidnapped thousands of other people during its eight-year insurgency, which is aimed at creating an Islamic caliphate in north-eastern Nigeria.
The government says more than 30,000 people have been killed, and hundreds of thousands forced to flee their homes.
Aid agencies are warning of a famine in the area, as people have not been able to farm for several years.