Derived from English folksong undoubtedly, but well naturalised in New Orleans (like St James Inirmary and Didnt He Ramble). Since blues is a subset of folk, it couldnt be blues without being folk. The question is,then, is it blues? McGrath correctly points out that it it hasnt got a blues structure, so you cant say "it is a blues". But it could be blues, or a blues song. St james Infirmary, to look at a very similar song in background and style, is often titled "St James Infirmary Blues", and I think most people would happily classify that under blues as well as folk. And when these songs were being formed into the music we know, the blues hadnt fully crystallised into the 12-bqqar form. Songs like Rising Sun, St james Infirmary, and Frankie and Johnny were rubbing shoulders with each other in the late 1800's, and it is a bit arbritary to separate them into different categories, because of later structural developments. So, personally, I'd say folk, and blues.