The statue description for Centered is:

"You gain Centered:
While using only wooden, leather, or no tools/weapons/armor you become Centered."

Observed behavior:
If I am holding no tools whatsoever, I am centered (or if I am using the handwraps). If I am holding a wooden sword, axe, or pick, I am no longer centered (my extra hearts go away, at least - I haven't been able to confirm if the rest of the effects disappear as well).

It may be that the ability to weild wooden tools and be Centered was unbalanced and changed at some point? If so, the tooltip in the Druid statue needs to be updated.

This is my daughter's favorite class, btw. :-)