it mentioned here:
3. Block incoming ICMP messages and any other incoming traffic with iptables or any of its frontends, such as ufw.
Well thats wrong check:
https://help.ubuntu.com/community/UFW#Allow_Access
By default, UFW allows ping requests . You may find you wish to leave (icmp) ping requests enabled to diagnose networking problems.
its better to block icmp on GNU using iptables rules not ufw.