Oh I think I’ve heard about this. Is a celebrant the same as a Humanist then?

No, a celebrant is different to a humanist.

It is not something I know too much about, however according to BBC Bitesize. It says:

Humanists do not believe in a god. They believe it is possible to live a good and fulfilling life without following a traditional religion. They do not follow a holy book either. Instead, Humanists value traits like reason and rely on science to explain the way things are. Humanists believe that people have one life to live - there is no afterlife. As a result, they focus on being happy and making the most of their life. They also believe they have a duty to support others.

BBC Bitesize