That's true, Mr Sandman. Sharp knew that some of the people he visited were referred to as 'Scots-Irish' (i.e. Ulster Scots), and that several of the ballads he collected were common in Scots collections such as those of Kinloch. Although he called his collection 'English Folk Songs from the Southern Appalachians' he stated that the British diaspora was most likely of Northern English and Lowland Scottish stock. However, he believed (at least partly correctly) that the ballad repertoire was common to both sides of the border and, like a number of writers of his day (and one or two even now!), used 'English' as a synonym for 'British'.

I also don't think it was the case, as dangyankee assumes from the Gemie article, that Sharp was interested - at least initially - in bringing American folk songs back to the UK. What he set out to do was collect songs of the kind he knew from his work in England. But, when he got there, he found himself picking up all kinds of other material of American origin (which Gemie doesn't acknowledge in his article), and that he did bring back, either in the published work or in his (much larger) manuscript collection.