I'm afraid you may be overestimating what the scene manager does.
It doesn't actually manage the content of the scene. Rather, it provides a framework that suspends generic crime reactions so they don't interrupt a scripted scene, and an easy way to re-enable this generic behaviour, add custom reactions to events interrupting the scene, and re-enable the behaviour again once the scene is over.
The behaviour within the scene still needs to be scripted separately.
If you need to keep track of whether a given scene is active, you can use
IF
DB_SceneManager((CHARACTERGUID)_NPC,_SceneName)
AND
[...]
THEN
...
to set a flag or a database entry and then clear it again
on
PROC
Proc_SceneOver((STRING)_SceneName)
AND
[...]
THEN
and
PROC
Proc_SceneInterrupted((_NPC,(CHARACTERGUID)NULL_00000000-0000-0000-0000-000000000000,_SceneName,_)
AND
[...]
THEN
...