There's a bit more to this than meets the eye, and the writers of the paper seem to have conveniently ignored some aspects of Bonilla's original descriptions. Bonilla reported the first as a small shining disk, almost perfectly round. The objects didn't just randomly cross the disk of the Sun, they crossed two-by-two, in pairs, in a dead straight line. Also, he calculated the distance as 242,000 km away.
Whatever he and his assistant were seeing, it was not a broken-up comet. Needless to say, the UFO nutter brigade has long held that Bonilla's observations and photographs are the first 'proof' of alien visitation in our neck of the woods.
Rather than fabricate some sort of scientific credence for the observations as a broken-up comet passing close to Earth, the paper writers would have been better off examining what else (physical or psychological) might have caused such an observation.
Cheers -