At this page:
https://github.com/youngmtool/ProgrammingBlockchain/blob/master/bitcoin_transfer/spend_your_coin.md

This sentence:
var bitcoinPrivateKey = new BitcoinSecret("cSZjE4aJNPpBtU6xvJ6J4iBzDgTmzTjbq8w2kqnYvAprBCyTsG4x");

Is cSZjE4aJNPpBtU6xvJ6J4iBzDgTmzTjbq8w2kqnYvAprBCyTsG4x a Base58 string or a Base58Check string?

IntelliSense shows it's a Base58.

If it is a Base58 string, is that generated bitcoinPrivateKey a Base58Check?

This code:
var bitcoinPrivateKey = new
BitcoinSecret("cSZjE4aJNPpBtU6xvJ6J4iBzDgTmzTjbq8w2kqnYvAprBCyTsG4x");
is for showing the simple way of generating a Bitcoin secret by using BitcoinSecret constructor and a Base58 string?
This has nothing to do with the above example code which starts with "var network = Network.Main;"?