Probably the most obvious explanation. I suppose that both attacking a diplomatic staff with a knife and just intentionally serving them contaminated food that

Probably the most obvious explanation. I suppose that both attacking a diplomatic staff with a knife and just intentionally serving them contaminated food that puts them on the toilet for a couple of days would lead to some response. If something that can be easily identified with technical means produces no diplomatic response, then, despite the consequences, it's not considered an attack. Seems to be part of the job description. Most likely, they couldn't even ask politely, behind the curtains, to stop that because the answer would be “Sure, if you stop doing the same, too”. And none of that can be discussed openly because of the secrecy of spying technologies, so they have to invent stories about non-lethal weapons when the case could probably be described as “Major Ivanov, increase the power until we get a clear signal”. When you start paying attention to these stories, it becomes clear that these secrets are kept first and foremost from the general public of the native countries, mostly for both public image and non-accountability privilege. It makes no sense to deny something that has been known to secret services of every developed country otherwise. It's quite ironic that before Snowden, military insurgents trained by this or that superpower, and mafia bosses who hired ex-special-agents had a more clear picture on, say, phone surveillance than law-abiding citizens.