I'm assuming you got the ending where Ghost decides he wants to give up the search. If you get this ending, the requirements are that you focus on the photos of Ghost. Ghost decides that he doesn't want to know what happened to him because he's afraid of finding out what could have hurt him, and thinks it isn't worth sticking around to find out a second time. Especially since Celeste is with him, he doesn't want to potentially get Celeste involved in something dangerous.
There are three other endings you can get depending on what photos you take and choose to focus on. There's another ending that involves leaving with Celeste, with different requirements to get it. All four endings are "correct" and none of them are meant to be a "canon" ending.