Though Kylo Ren had been in the town at the start, Ellie had never met him; she has no reference for Tai's ghost or mirage or whatever. What she does know is that the town likes to fuck with people. These ghosts in the fog? Yeah, she doesn't think they're real. Luckily for her, she's focused enough on Tai, this unfamiliar face, to have her own ghosts come to haunt her.

She finds Tai as the fog starts to clear and recede as he goes to follow whoever Ben is. But she knows there's no one named Ben in the town.

"Hey!" she calls. "Hey, wait! Don't go after that!"