No the argument hasn't shifted. The core point is that any time you use a piece of software, you have to have some level of trust towards the entity that gave you the said piece of software.

The way I responded to one particular example “what if I download Signal and compile it myself” is just that a particular example, not a shift in argument.

If you think there's no trust assumption in the distribution of software, feel free to provide actual arguments to refute that argument of mine, because so far your comments have been disappointingly lacking in substance.