IMO this is still a passive type of security through obfuscation. Active defence would be more like returning zip bombs to known intruders in order to crash the process.
It appears it can be configured to actively return attacks:
> Portspoof can be used as an 'Exploitation Framework Frontend', that turns your system into responsive and aggressive machine. In practice this usually means exploiting your attackers' tools and exploits
There's tons of client software that can be exploited if you send a dangerous payload to it. Think of an exploitable version of Curl that will fail if it receives a bad http header.
I would guess that it fingerprints the scanning software (e.g. metasploit), then feeds a payload back to it that has a known exploit in the scanning script.