Ping is a ICMP Echo Request (i.e. ICMP Type 8, Code 0). Incomimg packets are blocked in /etc/connman/firewall.d/10-block-icmp-firewall.conf or more precisely, all other ICMP packets are allowed over there, the chain’s policy is DROP:
IPv4.INPUT.RULES = -p icmp -m icmp ! --icmp-type 8/0 -j ACCEPT