I just noticed that you were using SkeletonMecanim, my fault.
When folders were used, the called method name was actually broken. I have just committed a bugfix and uploaded new unitypackages:
Spine Unity Download
The new version now supports a Spine Preferences entry whether to include folder names in the called event method name or not:
Mecanim Bake Settings
Include Folder Name in Event
"When enabled, Mecanim events will call methods named 'FolderNameEventName', when disabled it will call 'EventName'."
As the name "Mecanim Bake Settings" suggests, this setting has its effect when generating the animation clips, so you have to click Force Update Animation Clips
at the _SkeletonDataAsset
to have any effect.