Why does he think it came from inside one of the eggs? It is possible, worms have been trapped inside eggs. But I suspect something a little different.
To me that looks like a baby tapeworm. Tell him to look up photos online and see if he agrees. He can see more details than that photo provides. The hen has one set of plumbing for her egg laying system and a different set for her digestive tract. They meet at the vent. There is some separation when she is laying an egg to keep the egg clean but what I suspect is that a worm was down at the vent area when she was laying the egg and it came out with the egg.
To me this means he needs to worm his chickens. When this happens the worm load inside is enough to cause damage to the hens.
I notice that egg is cracked. I'd be reluctant to eat a cracked egg, maybe cook it and feed it back to the flock. But in general, if it were not cracked, I'd have no problems eating that egg as long as there was not a worm inside when I opened it.