It's really only confusing in this particular context, or to be precise, this particular sentence. Similarly, "Metropolitan Transportation Authority Invests Heavily in Rails" doesn't really make "Ruby on Rails" a particularly confusing project name.

Well, to be fair, Middleman translates authoring files (sass, yaml, haml, etc) into ready-to-publish static assets. It can also be wired to liveroad so that it instantly updates what you see in the browser. In that workflow, the name really makes sense to me.