I think the encounter you are referring to took place near Le Cateau, on August 25, 1914.
The German aircraft was identified as an Etrich Taube. This victory was also claimed (and awarded) to Lts. Wilson and Rabagliati flying an Avro. H.K. happily surrendered the small plaque that he and his observer had removed from the wreckage, saying "Your bird, I think."
This from Ralph Barker, "The RFC in WWI", p.39.
hth,
Will