The weird improv bit he/she is referring to was the middle part of Closure. I really like how they go off on one and indulge their prog selves, but I think the audience were more like,
If Opeth play Wacken again I think they should definitely gear themselves up for a heavy set.
Ideally they would have played at night and the selist would have been something like:
Wreath
Masters Apprentices
The Amen Corner
Godhead's Lament
Deliverance
That, my friends, would have ruled.