Well there was Oxygene and The Man Machine, too.
But in Britain - Gary Numan preleased The Pleasure Principle, which is perhaps better described as the first rock/pop album not to feature any lead guitars. While it's an electronic album, it still uses real drums, bass and violin.
Metamatic came a year after, but only featured bass, albeit heavily treated.
So it's funny, neither artist released the first all-elecronic album... I do indeed think The Human League pipped everyone to the post with Reproduction.
"Were' the Human League and there are no guitars (or drums...)"