I note that QuestionnaireResponse.author (the person who received and recorded the answers) allows Device, Practitioner, PractitionerRole, RelatedPerson, Organization, Patient). First, if a device is the author, the statement "the person who.." is not technically correct - it should be "the individual or device that received and recorded...."
Secondly, the QuestionnaireResponse.source does not include "device" as a reference. While generally a questionnaire would be entered into such a device by a patient, practitioner, PractitionerRole, or RelatedPerson, the device itself might enter answers to specific questions using SMART or CDS scripts to find and retrieve the answer. The use case may be rare or not yet considered but there is no reason a Device cannot be the source - and the provenance of the data entered by the Device would require specification as well. Such provenance should hopefully include the performer, subject and time of the resource representing that data element.