Ads usually have music in the background, those get included in the fingerprinting too. Besides that, the fingerprint consists of a number of time slices.
The actors personal Alexa will probably only fail if they try to use it with exactly the same millisecond-scale timing, exactly the same intonation, and with exactly the same background noise.
If it was like that then a home with some other source of noise (other music stream, someone speaking loudly etc) during the commercial would trigger the hotword. I guess that fingerprinting has to have some sort of tolerance anyway
The actors personal Alexa will probably only fail if they try to use it with exactly the same millisecond-scale timing, exactly the same intonation, and with exactly the same background noise.