I agree that it _should_ imply expertise, but it doesn't in practice. It bugs me because start using it as a status thing: "how to think like a senior developer", "listen to me because I'm a senior deveveloper". The title hasn't earned its credentials and it keeps getting used to fake credentials. Instead we should talk about good developers vs. bad ones.
Heck, I know someone who got the title of "senior" on their first job out of a bootcamp. They were credible in the sense that they had worked at other companies before and had a grown-up and dependable demeanor. But they weren't someone I would want to take coding advice from.