Yeah, I agree greenwashing is not the word here. I don't know what is, but if anything I would say you're trying to express something that is in an important sense opposite to greenwashing (greenwashing is trying to make something look good by falsely presenting it as eco-friendly, you're accusing something of boosting renewables by falsely presenting it as tied to them)

And yes, decentralization is the core aspect that is important, but renewables are importantly much more decentralized end-to-end compared to a diesel generator, because renewables, once in place, have no real central point of failure, while the supply chain for the diesel in the generator still has very important central points of failure that can be attacked (and explode quite easily due to the large amounts of flammable material they are carrying). Distributing the generation does help smooth over short-term disruptions but the overall throughput in the longer term can still be disrupted.

Also, while renewables might be out in the open, they are cheap and spread out over a wide area, which makes them pretty cost-ineffective to attack compared to more concentrated facilities.