Using the generic CallbackFunc is basically a single callback for multiple events. It's ran for every event that is listed, like Break, OnPickup, OnIgnite etc, but not all of these apply to all objects.
If you want only OnPickup, just check for it at the start of the function.
void OnStart()
{
SetEntityCallbackFunc("entity", "MyFunc");
}
void MyFunc(string &in asEntity, string &in asType)
{
if(asType == "OnPickup")
{
SetMessage("Messages", "NoteMessage", 0);
}
}
Similarly you can check for other types of events.