That doesn't make any sense, Steam does of course know if you own a game on Steam. Open Steam, check your libary, see your games. They also know if you are playing it. Unless you are using Steam in offline mode, which is pretty irrelevant since you need to be online to play Elite.
The API does have access to that data, it's the very same data. The API is provided by Valve themselves, giving out the same numbers you can see on the community HUB, again, provided by Valve themselves. SteamCharts is based on this data.
I am tempted to say the same thing.
First, you apparantly didn't understand the article. It is not about SteamCharts but about Steamspy, which didn't just display concurrent players like SteamCharts does, but also displayed individual user based data like hours spend in game, etc. This data is no longer available. The author of the article wrongly assumes at the end that SteamCharts relies on the same data, which is false. I've already shown you proof for that by linking to Valve themselves.