Here’s a quote from the BHA website:
“Humanists… ...make sense of the world using reason, experience and shared human values. We take responsibility for our actions and base our ethics on the goals of human welfare, happiness and fulfilment. We seek to make the best of the one life we have by creating meaning and purpose for ourselves, individually and together.”
The BHA website specifically says Atheists and Agnostics here but I think you can be a religious humanist as well, if you derive your moral code and your purpose in life as being separate from your religion.
I think part of the reason there are so many Jewish humanists is because “Jewish” is an ethnic description as well as a religious one. There are many Jews who follow Jewish traditions without being in any way religious.