The terms was applied to something that already existed. So yes there are other antecedents. Later techno does not entirely descend from Detroit, it descends from a greater history than just detroit.
This is the entire point.
If we only look at was used to first describe techno, then hardly any techno from the last 15 years can be called techno.
The word techno has been used by many many people to give a name to something that is transient, by it`s own nature for it to capture the zeitgesit, what defines it, will always be, and always has been, hard to define itself.
It`s like trying to define industrial (music). The word was used to give name to a type of music being made by a group of loose associates by an artist called Monte Cazzazza.
However, it didn`t really define anything as such and soon more music came to be made using this name, music that really didn`t sound like the music from this small group, as everyone needed a word to describe this rebellion against current norms and preconceptions, despite the fact that the music being made by all these people wasn`t really that related in musical terms.
Now what people refer to as industrial bares absolutely no resemblence and hardly any relation to what Cazzazza was describing waaaay back at the end of the 70`s.
A name was given to something that existed already. And techno is pretty much the same.
The main difference being that in techno there are bigger egos claiming to be inventors of it.