I spent a decade doing microprocessor validation at AMD & IBM a little more than a decade ago. Part of that work involved being around a lot of motherboards, many of them custom-built for testing of the cpu.
The size of this chip just does not ring true. A "chip" the "size of a grain of rice" would be VERY hard-pressed to have five wires attached. Even three would be tough. There is simply no way for such a device to sit across a standard data bus.
Moreover, the evolution of buses was definitely in the direction of point-to-point. Adding anything to a bus is going to blow it's specifications. Therefore, the addition of ANY snoop-chip to a motherboard is going to require significant changes to the design. And motherboards do NOT have room to just go adding buses.
So yeah, this story does not make sense, at a physical level, to any of the tens of thousands of us who have worked in this area if we address the matter skeptically. Moreover, there are probably hundreds of thousands of techs who, when they see the above paragraph, are going to agree. Finally, anyone planting such a story knows this.
So what are the options for the truth?
As mentioned, a larger chip does NOT make this story more credible.
Some earnest low-level type overheard something, freaked out, and reached out to Reuters. The more senior people that Reuters contacted, some of whom likely already had some sort of relationship with them, were so amused that they went along with it. I'm going to rule this out because, as other commentards have mentioned, Reuters is too valuable of an institution for that many people to toy with it.
Some reporter & editor at Reuters went on a bender. Again, this seems very, very unlikely. In fact, given the nature of the story, one would expect that a senior editor would have been brought in as well.
The "natural" explanations fail, and pretty badly. So let's talk about nation-state actors / TLAs. The size of the operation pretty well rules out amateur or small-time operations. Who is hurt by the operation? To the first order, Reuters and a major Chinese manufacturer. Second order, this stokes the brewing trade war with China & the US. It also generally strikes against international trade.
I would argue that these last two points point AWAY from the five eyes. Institutionally, they are heavily vested in globalism. The recent change in the US administration has not had time to penetrate the agencies to the depth needed to justify, let alone initiate and complete, an operation of this sort. While it is true the the US President can fire all of the US district attorneys at will (as was demonstrated by President Clinton when he assumed office), the intelligence agencies are simply more independent than people here seem to want to believe.