The vinegar removed only the shell of the egg because it was acidic. But it was unable to mess with the egg, because as it removed the shell of the egg, it was unable to get past the sac, the part that protects the inner egg. It is hard to puncture this sac, unless dropped or punctured by a nail or something hard.
I hope this helps. If you have any other questions, about this or any other question, just ask. I am here to help you. As needed.