Every time there's an article about machine learning or robotics, alarmists with no understanding of contemporary AI research start making allusions to Skynet.
Just because AlphaGo can beat a world-class Go master doesn't mean we're anywhere near strong AI. At the current pace of AI and neuroscience research, we're still centuries away from being able to develop an artificial sentience. That's like thinking that the invention of the fax machine means we're on the cusp of creating teleportation devices or that, because we can send rovers to Mars, that means in a few years we'll be colonizing exoplanets hundreds of lightyears away.
Yes, it's a step in the right direction, but it's an enormously small step compared to the difficulty of creating strong AI.
As for existential threats to humanity, we're liable to destroy ourselves through war and climate disaster long before we're able to develop sentient computers.