well you never know after it happened maybe the DD said something or gave him and a look and he said sorry so she dropped it
Even if he apologized afterwards...he did something which was very dangerous. He didn't just call her a name or pull her hair (which would have also been bad...but not
dangerous) Unless they were those blunt-tipped safety scissors, he could have easily cut HER along with her shirt! And he did it FIVE times. It wasn't like he got mad (or whatever) and cut it once and then regretted his burst of anger. I don't buy that doing something willfully destructive, not once, but over and over, can be brushed away with a "oops, sorry I cut your shirt FIVE TIMES."
Destroying her property is bad enough, but doing it while she was wearing it...raises the freak-out bar for me. If he'd cut her backpack or something, I'd still be mad, and might still expect it to be replaced, but the fact that a child could have been harmed (and someone else could be harmed in the future) is why I would bring it to the teacher's attention. She needs to keep a careful eye out (I know the teacher can't watch every child every second - but if she knows there's a problem, them she can take steps to prevent a recurrence).
By the way, I don't mean to imply the boy is "bad." He might have just been bored and started snipping away. I know my dd did this to her own pants once!

Believe me, we had a very serious heart-to-heart about the cost of clothes and what you can and cannot cut with scissors!