Anyone with an understanding of the current state of the art of both computer programming, and AI, understand why it's not sentience. The article said "sentience" not "thought", so we don't need to have a working definition of thought in this case.
Sentience is a stronger form of consciousness. Let's take the weaker form, since if you don't have consciousness you certainly don't have sentience. Consciousness is the subjective experience of "being like something". It is "like" something to be me. It is "like" something else to be you. The question is, is it "like" something to be the Google AI. Given we don't believe it is like something to be a laptop running a program, and AI is currently just (over-simplified but essentially) very powerful laptops running programs that have done a LOT of pre-computation to build themselves (basically just a whole lot of math) there is no reason to believe at some point enough math, or enough computing power, leads to consciousness. We did not believe Deep Blue was conscious even though its power exceeded that of a human brain by several orders of magnitude. This is because computational power alone is not the stuff of consciousness.
The same way 100,000 volts of electricity is a difference in magnitude from 1 volt, but not a difference in kind.