Continuity mistake: When Hector confront Ernesto just before he gives Miguel his blessing, he peels off the Frida disguise. But his beard on his chin is missing. It shows up in the next scene. (01:04:23)
Other mistake: Miguel was drowning in the swimming pool in De La Cruz's party but when he was thrown in the pit he managed to swim out of it.
Answer: No one really knows, perhaps the 'true' afterlife, though that is entirely speculation.