manager of bullshit that does little to no actual work

As others have replied yes the term was inspired by the rugby term but unlike a rugby coach who sets the teams strategy and game tactics, the scrum master in agile methodology is a tactical role that is focused on ensuring the team are observing agile ceremonies, sticking to their sprint commitments etc. What the team are doing and why is the responsibility of other roles like Product Managers who may also have Product Owners working closely with the teams whose responsibility is to have a prioritised backlog of items for the team to use as input to plan upcoming work. Usually there are higher level roles that set business level / market level strategy that gives guidance to Product Managers on where products should be focusing to meet specific business goals.

Unsure if a joke or not, but in the event of a serious question:

scrum masters are heads of scrum teams, their main purpose is facilitating good work conditions for the workers in the team. This generally means arranging and leading typical scrum meetings, helping workers do their job and shielding them from the Production Owner (the guy that decides what they are to make/deliver during a sprint . (sprints are 2-3 weeks long, where work is done according to a selection done at the start of the sprint and interruptions are kept low during that time.)

I don't want to say that it's an easy roles, but it's more a management type of role than a worker role. In my team the scrum master is also doing development work, since scrum master tasks alone aren't that huge with the way we do things.