without physically seeing it, my explanation would be. only one rafter was removed (cut) not much load bearing added to the other two. if he cut 2 or more rafters you would double the rafters to carry roof load. The double header is transferring load to the other two rafters, also some of the reason is the actual connection point, nails, hangar, safety factor, human screw up The load on the rafters is minimal, again based on my view of the picture, it is a cathedral ceiling which appears to be fairly steep, steeper roof less load on rafters. If their had been a 4/12 roof, stick framed, those rafters would be to small for roof load based on perceived span. Again all of this is based on a couple of photos.