Seeing that his eyebrow area doesn’t look damaged or scarred like the top of his head or under his left eye, I’d simply say that they escaped that kind of trauma to the area and so still grow the eyebrow hair back without issue.
One of my cousin’s once completely burnt off both of his eyebrows when lighting a bonfire (he’d thrown fuel all around it and the resulting fumes went up in a massive fireball when lit with him in it). To this day, he still has completely full and normal eyebrows 😉