What do you mean by coding?
Are you talking about the result after using getblockchaininfo on the Bitcoin core console.
I don't know if you can get or know the percentage of your current node syncing process but you should check the "blocks" that's the blocks that currently downloaded of your node.
Also, notice about initialblockdownload because if its true the node still syncing if false then it is fully synced.
About the 2nd question I don't have any idea how he knows if the users have multiple nodes and accounts but I think he would use time, median time and size on disk as a reference to know if you are using unique device, time and size. That's just my thought.
To understand what are those results of getblockchaininfo better check this link below.
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https://developer.bitcoin.org/reference/rpc/getblockchaininfo.html