What, did Russia run out of polonium or something?

They moved to novichock a while ago - which has more or less the same symptoms as mushroom poisoning.

more or less the same symptoms as mushroom poisoning

Only certain cholinergic mushrooms. Those are pretty rare. Usually kidney or liver failure which wouldn't present those symptoms.

Imagine you are a Russian doctor, you have a patient with severe nausea, diarrhea, blurry vision, headache, muscle weakness, and you don’t want to fall out of a window. What’s your diagnosis?

This level of conspiracy is too much for my credulity. I think Russia is a heavy handed murderous state, but I don't see the motive or means likely for this dude. I honestly believe it's more likely he's just an old guy that died from multiorgan failure from mushroom poisoning.

Remember Navalny’s poisoning and the wild theories Russian doctors were throwing?