This article seems to misunderstand Google's claims in multiple ways. This is clearly an anti-consumer practice but it's not a broken promise.

Any claims about how long a system will be supported have almost always been relative to when it first released. Apple, Samsung, and countless other consumer hardware vendors do this too. Those claims don't consider when the last unit of the same device model was manufactured or when the last customer buys one from "new" inventory, even though those should be very important factors for its lifespan.

Chromebooks have always been even worse than most in that respect: if multiple Chromebook models from different vendors have similar board hardware and the same CPU family (more accurately, using the same "platform" directory in the code), they're all considered one system in terms of lifecycle. Even someone who bought a brand new Chromebook model on release day might have already missed more than a year of its lifecycle before then, since new laptops sometimes use the previous year's CPU.

In addition, if you say a certain device will be supported with OS updates for 10 years, that doesn't imply that it'll still have the same OS with the same branding the whole time. They never guaranteed every update will remain compatible with every piece of software you use on it, either. A Chromebook from 2016 that could run uBlock Origin and NaCl apps then won't be able to run them after installing all current OS updates in 2026.