Not sure if you're aware but it's not that uncommon for people to be interviewed when someone else already has the job, or they don't actually end up hiring. Maybe someone internal got the role and they still interviewed to meet HR requirements. So even if you did "the best interview ever" you're not guaranteed to get the job.

I remember going for an interview in London at the start of my career and all the candidates were in a room together beforehand talking and doing some group exercises. One of the candidates parents was best friends with the interviewer and knew several of the team and they weren't too shy about talking about it. It was pretty obvious she'd be the one getting the job!