This may, or may not be the case in your instance!
But, as every mains socket and FCU has an earth connection, it is considered best practice for fixed appliances such as extractor fans, mains thermostats, or alarms to be supplied with a cable wih an earth.
This means that a fully plastic item that doesn't need an earth connection, may still have an earth terminal - just to avoid a loose earth lead flapping about the enclosure, possibly causing a short.
And due to this possibility, manufacturers will often say that the device 'must' have an earth connection, even if it isn't used!