It was a controlled poisoning.
He did kill the guards who were keeping an eye on Jesse, though.
But frankly, I still am on Walt's side because he's a hell of a character. Don't know how you can't admire him. He's a genius, he's a tactician. A fucking mastermind you don't wanna cross. But at the same time, I remember him from season one, and all of the shocking displays he's seen. Being held at gunpoint by Emilio and Krazy 8. Making the decision to kill Krazy 8 before trying so desperately to persuade himself to let him free. And then crying/apologizing afterwards. The looks of awe and disgust on his face after watching Tuco beat someone to death. Looking at Jesse, knowing Tuco has wronged him. Yeah, Walt has broke bad. But he's learned that in this business, there is no way of surviving being a goddamned pussy. And with that considered, I think he's done a pretty good job at being a good enough guy. And that's good enough for me. I'm with Walt to the end. Fuck all else.