If it appeared then that’s concerning. Can you get a better picture? It could have been mostly absorbed but then prolapsed. It looks more like yolk than intestine but it’s a bad picture so I could be wrong.
Yep, looks like a yolk sack. Do everything you can to keep it from rupturing because if it does, its chances of survival are virtually zero. Keep him from moving as much as you can without making him struggle to try and get free.
If he'd just hatched I would recommend carefully sliding him back...