My interpretation: "Web device" implies a device that allows browsing the web (such as a smartphone or tablet). "open" implies that it is open source to some

My interpretation: "Web device" implies a device that allows browsing the web (such as a smartphone or tablet). "open" implies that it is open source to some extent (similar to Android). "based entirely on web technologies" differentiates it from Android in that all apps are web apps and use standardized web APIs to access the hardware rather than having native apps that use proprietary APIs. It does seem weird that the sentence use the term "OS" to describe devices, though.