They're not a fake metric. Sure, ratings can be gamed and are gamed. But ratings and accompanying reviews inherently aren't fake, and are the closest proxy to "word of mouth"
What you might be missing in your interpretation is that “fictional,” didn’t mean what you’re saying it does.
The OP meant that the app ratings aren’t a measure of a tangible quality or effect. Like “heat,” or “number of tickets.” The unit of measure and what it means is “fictional,” in the sense that the scale and units are completely made up and arbitrary.
They’re not saying that it’s fictional in the sense that it doesn’t exist or isn’t real.
They’re aptly noting that by forcing developers to optimize for this rating system, app stores are incentivizing developers to support only the most recent OS releases and deprecate support for older devices.