If you watched the movie he said it was a feeling he had for only a second. It was the lure of the dark side his family is plagued with. He resisted but Ben woke up and misunderstood what was going on. They literally explain and show that in the movie.

I think Summons sums it up pretty well. For me, it's that through line of 'fear', being the curse of the Skywalker line. For even just a split second, Luke is so afraid of what Kylo might become he considers taking a dark course. It's ironic. He turned away from the Darkside, just like he did with Vader, but in this isntance it was just enough to set Ben Solo off. It's actually brilliant. It really fits with the themes of the saga and it sets up the guilt and reasoning Luke has for exiling himself. The Jedi had flaws, they had too much confidence in the Lightside. His status as a living legend put him at risk of the same fate. It only takes one moment of weakness to shatter trust. It's a powerful lesson. Never let your guard down... don't give in to fear... Because even good people, the best people, do terrible things because of fear. Message of the saga and very much what Lucas would have wanted.

Thing is we don't really know Snoke is. He's the leader of the first order and learn force powers from who? Snoke is completely underdeveloped.