Why does everyone insist she can't be missing?

“Ross, Fiona’s parents have hired me to find her. She’s missing. As her ex fiancée, you might have valuable information that can help us find her as you will know…”

Ross cut her off. “Fi’s missing? Are you sure? I just saw her last night, how can she be missing?”

Pen in hand and taking notes Katie continued, “When and where did you see her last night?”