OpenWrt is a Linux distribution (like Ubuntu, Fedora, Debian, etc.) that we are using as the OS on Tessel 2. For the most part, you don't have to deal with it, but it's good to know what's underneath when doing things where there aren't pre-made libraries.
In any programming language that is capable of reading files, including Rust, you will be able to open
/dev/input/event0 and read a stream of events consisting of a timestamp, a keycode, and whether the key was pressed, released, or repeated.