A South African think tank, the Institute for Security Studies, says it believes that the release of 107 youngsters - 105 schoolgirls and two young boys - by Islamic group Boko Haram was due to their religious background. In an interview with News24, ISS senior researcher Martin Ewi said the group realised their mistake after the abduction of the Dapchi girls in north-eastern Nigeria last month. He said the Boko Haram group which had abducted the girls was ideologically different from the Abubakar Shekau led faction, which did not discriminate on who it kidnapped."Well, the first thing that you need to look at is who had abducted the girls. The [Abu Musab] al-Barnawi group is not known for violence on civilians especially Muslims. The group's incentive to kidnapping the girls in the first place was what the government gave to Boko Haram over the Chibok girls who were mostly non-Muslims, but as soon as they realised that these ones [Dapchi girls] were Muslims, they change their heart," said Ewi.The kidnapping of at least 110 school girls in Dapchi last month had raised questions about the military's repeated claims that the Islamist militants are on the verge of defeat, after nearly nine years of bitter fighting.It had also revived memories of the 2014 mass abduction of more than 200 schoolgirls from Chibok that shook the world."The military was caught off guard in Dapchi and the girls kidnapping raised questions over the government's consinstant claims of defeating the group. Every time the government says it has defeated the insurgents, they come back and carry out massive mass atrocities, which I think is their way of showing the government they are far from being rooted out," said Ewi. KEEP UPDATED on the latest news from around the continent by subscribing to our FREE newsletter, Hello Africa.FOLLOW News24 Africa on Twitter and Facebook. Late last month, terrified pupils fled the Government Science and Technical College in Dapchi, Yobe State when heavily armed fighters in military fatigues and turbans stormed the town, shouting "Allahu Akbar" ("God is greatest").The authorities initially denied that any student had been kidnapped.But, a week later President Muhammadu Buhari apologised to the girls' families, saying: "This is a national disaster. We are sorry that this could have happened."The girls were, however, released last week in what the insurgent group described as "pity"."Both Boko Haram groups are violent, but only differ on their target. The Shekau group doesn't discriminate on who it launches attacks or kidnappings against. "The other group which has more links with the Islamic State often targets the military and non-Muslims who they regard as infidels, which I think explains why they had kidnapped the girls in the first place. They assumed that they were not Muslims which is one of the reason they later released them," Ewi added.