They aren’t the same, although they can intersect. It’s easy for us to assume that because we feel challenged, we are fulfilled. This isn’t the case, much as being busy doesn’t mean we’re having an impact.
At different times in our lives, it makes sense to lean in one direction or another. Sometimes we’ll do unfulfilling work that challenges us for the sake of growth, and other times we’ll do unfulfilling work that doesn’t challenge us because it matters.
If you have to ask “does this challenge me?”, it doesn’t. Freely substitute “challenge” with “fulfill”.
It’s okay to not have both or to lean to one side. Issues arise when we aren’t aware of and honest about the distinction between the two.