The arrested man was bailed on Friday pending further enquiries.
Police are continuing to appeal for dashcam footage of the incident.
Detectives said “a lone man” threw a substance at the teenagers before fleeing on an electric scooter along Harrow Road.
Corey McFarlane, Teagan’s father, previously said “words could not express the shock, pain, and trauma” his daughter is going through, “both physically and emotionally”.
He added that she was initially discharged from hospital, but was later readmitted.
The 16-year-old boy was treated at hospital and has now been allowed home.
