You can argue about whether he intended to hit him in the face, but that doesn't really matter. He swung with intent. He swung high. And he absolutely smoked Stewart, and his reaction -- while also not acceptable and deserving of a suspension in its own right -- was certainly understandable.
How long will LeBron's suspension be? Based on precedent, my best guess would be two to three games, and I would lean toward the two. You can at least argue LeBron didn't fully intend to hit Stewart in the face (though I'm not sure what he thought was going to happen swinging that high within that proximity), whereas in the 2018 Rockets-Lakers brawl (video below), Brandon Ingram, who got a four-game suspension, and Rajon Rondo, who got three games, both threw clearly intentional punches to the face.