Ah, that's a race condition, something that Rust doesn't protect against in general (it's fairly difficult: whether a piece of non-determinism is a race condition depends on the semantics the programmer desires). A data race is more specialised, and we try to be careful to use "data race" when discussing this aspect of Rust.

http://blog.regehr.org/archives/490 has a fairly good discussion of the generally accepted definition of data race.