The Alexa listens for a keyword (Alexa, or it can be changed to Amazon) locally, and then once triggered sends your query to Amazon for processing. That's the same way that "Hey Siri" and "OK Google" work.
Samsung seems to have skipped the 'trigger phrase' part and just sent EVERYTHING and tried to see if it needed to be listened to.
i expect amazon intends to obtain acceptance by not copping to the fact that it also has to be a microphone.