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ICMP type 3, code 1 messages (Host Unreachable) are usually sent by the router that has an interface in the subnet of the host you are trying to reach when that host does not respond to the ARP request sent by that router. This means the host is not available on the subnet. I.e. it is unreachable.
If the source IP address of the ICMP host unreachable message is the same as the destination of the initial packet (both are listed as "SITE IP" in your output), then maybe there is a loadbalancer involved that chooses to send the unreachable this way, but it might also have other reasons.
