[gus_massa]

(I still don't discard the joke hypothesis.)

It's a stone statue over a glass shelf, so the friction coefficient is probably low and it's possible that the vibrations make it turn around.

Perhaps before the shelf was inclined a few millimeters to the other side, so it didn't turn.

Perhaps it was formerly in a wood shelf, with more irregularities and a bigger friction coefficient.

Perhaps there was no camera, so when someone found that it was looking to the other side, they just assumed than someone else had moved it.