I'd say both, though low-level is more specific to compiled Common Lisp implementations rather than general for all of lisp family.
Specifically, ANSI Common Lisp is equipped with a function called DISASSEMBLE, and on many implementations it will provide you not only with plain assembly dump, but also with comments regarding said assembly, for example a comment specifying "we're calling X here", "this is handler for single parameter, and this is for multiple parameters" (in case of optional arguments to function)
Computing in the theoretical sense, right? I've always heard the opposite of this claim: Lisp abstracts away how computation is done on actual hardware. Isn't that what the famous Alan Perlis quote was referring to?