Better to be safe than sorry
The report on the BA intranet gives a clear picture of everybody taking a rightly cautious view of a "suspicious" article on this flight. There will have been strenous efforts made to get the passenger(s) to claim the item but if nobody comes forward what would you do? Bear in mind the contents were not known until after landing and we are not dealing with an obvious "washbag".
No doubt the person who lost this on board will be feeling very sheepish for not owning up but is hardly likely to come forward now for fear of a very large bill!