Slide guitar in India goes back to the eleventh century, played with a glass ball. There are some African instruments, then there is the whole Hawaiian thing, which comes down to one or two people having invented it. However, things get murky because there were travelling Hawaiian groups in the south and some black guys went and saw that and started playing slide because of that. Casey Bill Welton, a slide guy from the 30s, called himself the Hawaiian guitar wizard and played it flat on his lap. So did Oscar Woods, so did Black Ace, and even Charlie Patton, on a couple of tracks.
Delta blues open G tuning is exactly the same tuning that is the main tuning used in Hawaiian music.
It's also the tuning Debashish uses, it's also found in the Phillipines, Mexico, the Caribbean, South America. It's almost the universal tuning of colonial musicians. Open G is the tuning that makes an open chord that you can get to with the least amount of string changing from standard tuning. All these cultures arrived at it separately. Because I'm interested in linguistics, and the spread of languages, that's all tied in with the music.