It is one of the Mysteries of Roku, it seems.
Me, Myself and My Members... Maybe?
I had asked couple of Co insiders but even they had no clue - one proposed it was after somebody's first name.
"Self" is also a popular - perhaps more popular than "this" - choice in languages. One thing is for sure - "m" is shorter and easier to type. If it were me, i might have chosen underscore "_" as the special variable (so a good thing it wasn't up to me, ey? we save one Shift press now).