i bet if you gave it a good thrashing up to the mot station and they tested it without turning the engine off that would go through, i see it all the time. sometimes just holding it at 2000 rpm just isnt enough to clear the system out or get the cat hot enough.

also there is nothing to say he revved it at all, it just says manual observation. a common trick is to let it go through on idle and if it fails try and sell you a service etc