I always thought FISO were supposed to keep a lookout for traffic within the ATZ, it seems a tower visitor was more vigilant in this case
Unfair I think. We have no idea what the FISO workload may have been with radio and other traffic. An aircraft that should have been well above circuit height until crossing the runway centreline would not normally be a a candidate for close observation (the tower at Shobdon is always dead-side and not best positioned for such observation anyway).