Small correction: goes back to the mid-90's as a distinct thing, and you could hear that type of beat in songs even earlier than that. DJ Shadow brought it into general consciousness with his 1996 release: Endtroducing, but others were doing similar before. Back in the mid-to-late 90's, we were calling it "Trip-Hop". Though that was a broader term than lofi, which seems more specific.
Maybe the ultimate origination were in groups like De La Soul and PM Dawn. They had vocals, but their beats were often super chill.
I would disagree that Trip-hop is more broad. Trip-hop seems much more specific.
As far as Endtroducing being the first instrumental hip hop album, I guess one could argue that. However, it's a bit like saying that Iggy Pop and the Stooges were the first punk band. Either way, even though both movements come from an earlier time it didn't get much attention until the following decade. It would be akin to arguing that grunge isn't a genre from the 90s because Dinosaur Jr. was around in 87.
This sound goes back to the early aughts when it had it's roots in underground hip hop.