Right. If it's ended up on a production board that means one of two things.

1. They intend to use the microphone in the future

2. They disabled the microphone after having the boards manafactured right before shipping - what changed?

If they knew they weren't going to use it, why didn't they leave the microphone unpopulated? It would save on their BOM cost too, there had to be a reason.

In this instance, the microphone was discovered when Google added built-in 'Google Assistant' support to the 'Nest Guard'.

So yes they planned to use the microphone in the future, to do precisely what they have done here.

This is the most accurate explanation. In other words, it's a mic like any other. The 'disabled' in this context means nothing. Just wait till Google gets served with a warrant. Suddenly, those mics won't be disabled anymore.