You have it spot on – someone is sitting watching the game and writing updates as they happen and sending them out.
Think of someone sitting writing updates on a Facebook or WhatsApp group message.
The reason these will update differently from things like a TV broadcast are down to the delays in some broadcast systems – the processing and transmission of the broadcast can take slightly longer using some systems than others, so one signal may take a few seconds longer to appear. Some broadcasts also use a purposeful delay to allow the network some control (the ability to preview and stop a broadcast if needed) or to add in subtitles or other information.
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