As jahonix mentions, any software that wants to put in a url to pool in their software as default is asked to create their own unique fqdn for the pool, etc. So this is pfsense playing nice with ntp.org
http://www.pool.ntp.org/vendors.html
Anyone smart to even look into where or what its using for ntp should prob change this to either their own ntp servers of choice or the fqdn pool urls for their region of the globe.
For example if you want to use the pool and your in the US you should use say
server 0.us.pool.ntp.org
server 1.us.pool.ntp.org
server 2.us.pool.ntp.org
server 3.us.pool.ntp.org
You can find a full listing here
http://www.pool.ntp.org/zone/@