Tencent isn't claiming ownership of these strings, it's claiming that strings with a particular format have special meaning wrt. Tencent's APIs. It has told Github about that format.

This is fundamentally similar to how UPS, DHL etc. document how to recognise their tracking numbers.

"Their" and genitive in general doesn't necessarily mean ownership. It's often used for various sorts of connection. For example, "my address" doesn't claim ownership of either the street or the house, "my age", "my wife", all connected to me somehow but not owned by me.

Not your random string not your coins. Not your random string not your monkey picture.