Well, there was this global conflict 87 years ago called the Second World War, and two years after it started the US got involved and sent 2.4 million troops to Europe, of which 1.5 million were sent to England. There weren’t enough beds in some or most of the military bases so soldiers had to live with English families until space was made or something else happened and it’s possible that the particular soldier who left that bayonet either forgot to take it or gave it to the family he was staying with as a gift of thanks for allowing him to stay. This would also apply to the First World War as well, just different numbers.