That is capped brood.
OK, thanks! So, what did he do, sacrifice some brood for the operation?
Terri when doing a cutout, I for one try to preserve as much brood as possible, when possible. In this case I see the advantage. To answer your question; Yes he did sacrifice some brood in the places where he made the slits for the purpose of inserting he the prepared fishing line within the frame as shown.
The trade off advantage here is taking into consideration newer comb is soft, this procedure will help insure the transferred new comb will stand a much better chance of staying in place,
not sagging, by giving the extras fishing line support, reducing the dreaded sagging of the comb. He also ties twine around the comb to help it stay in place as well.
(I have used rubber bands.) This will give the bees a fighting chance vs time to reattach/secure the new comb to the frame itself, hopefully before the catastrophe of drooping/sagging wax happens.
Phillip