A bunch of things a compiler "going downwards" needs to do don't apply, e.g. you don't need to worry about registers and things like that. And there's potentially more complex concepts to map to instead of just breaking source-language concepts down.
Haven't seen that terminology applied to individual passes.
It was just an example of a task. Also, "compile to LLVM" is very much "LLVM is part of the compiler, and thus worries about registers". Compile to C is (depending on source language and exactly which definitions you use) potentially also a transpiler.
Graal for example is a compiler but not a transpiler.
Just like all cheese burgers are burgers but not all burgers are cheese burgers. Nobody questions the term ‘cheese burger’ because we already have the word ‘burger’.
Yeah, because a cheese burger has cheese. What does a transpiler have? What is the common factor between all transpilers? Who decides on this layering of which languages are higher level or lower level? C2Rust doesn't call itself a transpiler, it calls itself a translator.
Haven't seen that terminology applied to individual passes.