Thanks for raising a question on Alexa’s (Amazon Echo) AI/Machine Learning aspect. My deduction of Alexa’s machine learning abilities comes from a Quora answer on Amazon Echo. Former Amazon SDE mentioned the use of “exoctic” machine learning algorithms used in Echo.
I researched more , and I don’t think its just a voice operated querying of database like you mentioned. I am not claiming that Alexa uses machine learning as heavily, but it is definitely a part of it.