The police officer leading the investigation told Swedish media on Thursday that his team had seen evidence which showed that the assailant "struck a blow with his sword" on the pupil.
"He was lucky and was hit on the arm, not by the sharp side but by the more flat one," Chief Inspector Thord Haraldsson said in an interview with the Gothenburg Post.
The inspector explained that the boy had experienced "pain and swelling" but said he had avoided needing hospital treatment.
Doctors are still treating the other student injured in the attack, who was moved from intensive care to a regular ward earlier this week. The teacher who was attacked is understood to remain in a "serious but stable" condition, according to Sweden's biggest news agency, TT.
A cafe which is part of the Kronan school complex where the stabbings took place reopened for the first time following the violence on Thursday.
Staff and students who stopped by "hugged, cried a lot, talked and tried to grasp the situation", Peter Asp, a spokesperson for Trollhättan council, told TT.
Trained counsellors were also on hand to offer support to pupils, who are scheduled to return to classes on Monday, following a scheduled autumn break this week.
Asp said that security staff currently guarding the building were set to remain on the site.
The 20-year-old died after throwing himself at the sword-wielding masked man in a bid to disarm him as he entered the school.