"All mean the same thing - plate at bottom of wall that is bolted to slab." Only on houses/buildings with monolithic slabs. Not on a building with a foundation and floor joists. On these structures the plate at bottom of wall is nailed/screwed on top of floor structure.
speaking as a builder the sill plate would be on the top of the foundation wall and would be at least a 2x6. i have never seen a 2x4 plate on top of a foundation wall. Most houses have foundations with floor joists so it is logical that the software defaults to 2x6
As a Designer and Builder that bedroom would be 120SF for figuring framing, flooring, drywall [plus the closet], insulation. For tax and real estate purposed it would be listed at 10'x12' or 120SF.