I figured out what was going on and I am posting here in case anyone else has the issue and can use the information…
It turns out the black arrow pointing to the left in the interface column in the firewall log means that it is a communication that is OUTBOUND from the WAN interface itself, not from a host using the WAN interface. This was happening because I had created a separate VLAN (say, VLAN5 at 192.168.5.0), assigned an Access port to it and set it as that port's PVID. I had then connected a LAN port on a Linksys 4-port router to that port on my L3 switch thinking that the Linksys would just act as a dumb switch and allow the wireless clients to connect.
What was happening is that a wireless host would communicate OUTBOUND, and the external host would reply but the NAT on the router was routing the reply back to the WAN port on the firewall (since, to the Linksys, the initial communication came from there) rather than the internal host that had initiated the conversation. When the WAN port would attempt to reply, the default block rule blocked it and it was logged. That's why it continued to block and log it even after I set a rule, as a test, allowing the WAN port to communicate externally to any IP using any protocol.
To fix it, I reflashed the router using DD-WRT which allowed me to set it up as a true dumb switch, which also allows wireless clients to connect and seem to the rest of the networks like they are simply hosts physically connected to one of the physical ports. Now the router does no NAT, the WAN port on the router is disabled and everything is working as it should. Thanks again to marvosa for the time and assistance.