I think they did a bad job at connecting ricen cigarette pack > saul > WALT TRIED TO KILL BROCK
but whatever.
I thought it was fine.
Jesse initially believed that the ricen cigarette was taken from him to poison Brock when he was frisked by Huel in Saul's office, and was no doubt reminded of this incident when Haul managed to swipe his weed from his jacket in similar circumstances. Thus, when he looked at his cigs after noticing his weed gone, he was reminded that Walt had the
opportunity to take the ricen cigarette from him. What changed is that he now realized Walt has the
ability to do it and the ability to manipulate Jesse even if it meant harming a child. He was initially convinced by Walt that Gus poisoned Brock because Gus has been shown to be OK with the murder of a child in the past. Jesse eventually realizes that Walt is no different than Gus in this regard after Walt's reaction (or lack-thereof) to the murder of the boy on the dirt bike. Finally, the scene in the desert further reinforces that Walt is manipulative and will do anything to protect himself, including killing Jesse, and that Jesse knows this.
