On "no route to host" error fping 3.5 incorrectly prints line "<host> : 0 - - -" and return retcode 1.
Zabbix ignores this retcode and assumes that first ping was OK with 0 ms RTT, host alive.
I think zabbix should check fping retcode, it's result of pclose() call in libs/zbxicmpping/icmpping.c:70.

1. fping -v
   fping: Version 3.5
   fping: comments to [email protected]
2. ping -c2 -W1000 172.16.3.1
   PING 172.16.3.1 (172.16.3.1): 56 data bytes
   ping: sendto: No route to host
   ping: sendto: No route to host

— 172.16.3.1 ping statistics —
2 packets transmitted, 0 packets received, 100.0% packet loss

1. fping -C2 -p1000 -t1000 -s 172.16.3.1

172.16.3.1 : 0.00 -

1 targets
0 alive
1 unreachable
0 unknown addresses

1 timeouts (waiting for response)
2 ICMP Echos sent
0 ICMP Echo Replies received
0 other ICMP received

0.00 ms (min round trip time)
0.00 ms (avg round trip time)
0.00 ms (max round trip time)
0.002 sec (elapsed real time)

1. echo $?
   1
2. fping -C2 -p1000 -t1000 10.0.0.1
   ICMP Host Unreachable from 10.0.22.1 for ICMP Echo sent to 10.0.0.1
   ICMP Host Unreachable from 10.0.22.1 for ICMP Echo sent to 10.0.0.1

10.0.0.1 : - -

1. fping -C2 -p1000 -t1000 193.0.0.193

193.0.0.193 : - -