On the Z22XE the down-pipe from the manifold normally has two cats. A smaller pre-cat visible in the engine bay immediately downstream of the first lambda sensor. The larger main cat is further downstream just before the center silencer boxes.
If the car is Norwegian market maybe less onerous emission standards applied when new, but I would have thought it unlikely. More probable that the car was built like all the others to be Euro IV compliant.
So if you only have one cat in the down-pipe but two lambda sensors then somebody has cut out one of the cats, likely the upstream, and bridged the gap. Might it be that the square welding in the main cat is a patch to fix a hole? The other possibility is that somebody has fitted an earlier 2.0L down-pipe, but these have only one lambda, but easily modified.
It might help if you could get the tailpipe emissions measured? And a trace of the lambda signal and the fuel trims.