A trivial question on the meaning of "relatives" in an article on horizontal gene transfer
You are correct. 

From the author's point of view there is not much difference, however. Phylogenetically speaking 'species' are kind of artificial distinctions that exist only as sets of individuals and don't usually convey information, so it makes sense to forget that species exist when talking about HGT. Hopefully that helps provide context for why such imprecise wording is so common.