How to Disable Airport Sniffing?
If you run airport without arguments it just prints a description of its options and examples of how to use some of them, including airport en1 sniff 1 to start sniffing. It does not report the current state of the interface.

To actually start sniffing you need to call the command as shown (and replace en1 with your actual WiFi interface):

$ sudo airport en1 sniff
Capturing 802.11 frames on en1.
^CSession saved to /tmp/airportSniffHZ3nqn.cap.
$ ll /tmp/airportSniffHZ3nqn.cap 
-rw-r--r--  1 root  wheel  24 Nov 26 10:10 /tmp/airportSniffHZ3nqn.cap


It will keep running (and capturing) until you press Ctrl-C. To analyze the captured data you can use tcpdump or Wireshark.