it was kinda weak. he checked, realized he didnt have his weed, then pulled out his cigs and, now knowing that walt killed mike, realized that walt was the one that had the gorilla pickpocket the ricin cigarette, not gus.
pretty big leap imo. the weed in the office was purely a plot device for him to figure that out. my only complaint
Weak to the viewers because for us Brock's poisoning was two years ago. The fact that the vast majority of posts trying to recall the ricin/LOTV incident at the time of Sunday's episode had huge errors in them is proof of this.
However, for Jesse that was only a few months ago AND he's been obsessing about it/the boy in the desert/his suspicion that Walt is playing him THAT WHOLE TIME. Given that when it first happened his initial suspicion was that Walt had Huell lift it and then poisoned Brock himself (exactly what actually happened) it isn't hard to believe that he went back to his initial conclusion.
The fact that Walt didn't actually use the ricin is irrelevant. Jesse immediately knew Huell took his weed, which confirmed in his mind the initial theory when it first happened that Walt was playing him. Then all he had to do was realize what the odds were of Walt lifting the ricin and then Brock just happening to get poisoned accidently at the same time and he's got it. He already believed Walt was playing him, he already knows he's lying about Mike and he had already suspected in the past the truth of what actually happened. Honestly, the cigarettes made it a little TOO obvious. It wouldn't have been any less of a stretch for him to just realize once he knew his weed had been lifted what happened. The writers clearly put the cigs in there to not leave any doubt for the viewer and many STILL didn't get it.
IMO, people upset about this are one's who just don't remember the series as well as they thought they did and are now trying to preserve their pride by saying it doesn't make sense. It makes absolutely perfect sense.