I’d suggest you read the article. He was in Russia to meet with Russian intelligence, presumably to discuss whatever it is that the CIA and Russian intelligence have to talk about, which the article describes as a common thing for CIA agents to do.
This opening line? Where you say he was an undercover agent? Even though the article explicitly states he wasn't? I mean, that's why I suggested that you should actually read it.
Yes. I'd suggest you read up on what a hypothetical situation is. Also, did you notice where I wrote about American spin? Yeah, I'd highly suggest reading that part too. :)
Sounds like a default setting when operating on foreign soil
Poisoning is not that hard when you're a nation state. Light coat of magic dust on your door handle is just one of many methods.