Earlier quoted context omitted.
The computer and the program wouldn't exist without us, though. They only exist to be interpreted by us. The physical properties of the circuits outside of what we cajole them into doing are irrelevant, meaningless. The circuits only do their work regardless of particular interpretations; they wouldn't exist at all without people building them to be interpreted.
The physical computer could exist regardless of us. The program, if by that we mean "a human model of the computation happening in a physical computer" is just a description, yes. It would be extraordinarily unlikely, but physically conceivable, that a physical system that is organized exactly like a microcontroller running an automatic door program, together with a solar panel, a basic engine, and a light sensor, co…
What you say about buildings is sort of true as far as it goes, but irrelevant for the argument because buildings aren’t symbolic manipulation machines that only mean something via conscious interpretation, that some people are claiming could gain consciousness themselves.