That design doesn't stop them from adding a discrete Off by a firmware change. It just makes a discrete On much harder. Depending on some design details, even a discrete On might be possible.

If the processor can control the behavior of the power toggle command while it is on, then even discrete On is practical by adding a command that means "ignore the immediately following power toggle". That command followed by power toggle could be a discrete On because when the processor was off the IR sensor board can't ignore the power toggle and would turn on, but when the processor was on it could ignore the the power toggle.

Of course none of that means you're likely to convince them to make a firmware change they don't want to make.