UGameInstance init when project is opening

Like the document says, "In Editor mode, which is used by Play In Editor and Simulate In Editor, a different flow is used. The engine initializes and starts immediately, as it is needed to run the editor, but creation and initialization of objects such as the GameInstance are deferred until the user presses the button to launch the PIE or SIE session. "

I write a class extends UGameInstance, and override Init function. when I open the project, the init() function just be called. And int the Editor, when I press the Play button, it also calls the init function. I think it is wrong, or Did I understand it wrong?