This is actually the first thing I got confused with after I installed my a lightning node for the very first time back in 2018. c-lightning ships with two (actually more) programs
lightningd
lighthning-cli
lightning-cli is a command line tool that sends commands via JSON RPC over a unix domain socket to lightningd so if you type: lightning-cli help what actually happens is that you send the help command to lightningd this will give you a list of all commands that lightningd can accept.
This is different to the command line arguments that can be given to lightning-cli which you are asking about. You can get the command line arguments by typing in lightning-cli --help. My output looks like this:
lightning-cli --help
Usage: lightning-cli <command> [<params>...]
--conf=<file> Specify configuration file
--lightning-dir=<dir> Set base directory: network-specific subdirectory is
under here (default: "/home/user/.lightning")
--network <arg> Select the network parameters (bitcoin, testnet,
signet, regtest, litecoin or litecoin-testnet)
(default: bitcoin)
--mainnet Alias for --network=bitcoin
--testnet Alias for --network=testnet
--signet Alias for --network=signet
--allow-deprecated-apis <arg>
Enable deprecated options, JSONRPC commands, fields,
etc. (default: true)
--rpc-file <arg> Set JSON-RPC socket (or /dev/tty)
(default: "lightning-rpc")
--help|-h Show this message. Use the command help (without
hyphens -- "lightning-cli help") to get a list of all
RPC commands
-H|--human-readable Human-readable output
-F|--flat Flatten output ('x.y.x=' format)
-J|--json JSON output (default unless 'help')
-R|--raw Raw, unformatted JSON output
-k|--keywords Use format key=value for <params>
-o|--order Use params in order for <params>
-N|--notifications <arg> Set notification level, or none (default: info)
--version|-V Print version and exit
From there you can see that the -k argument stands for keywords
-k|--keywords Use format key=value for <params>
For completeness there is even the possibility to get the command line arguments for lightningd by typing lightningd --help which gives you basically all config arguments and additionally the plugin system can append command line options.