So I came in this morning to a machine in Miami connecting through Missouri and out to a 3rd WAN location.

I'm trying to figure out what is going on. I have closest server rule for Miami to use the Miami satellite which is up, fall back to Missouri and nothing else.

Do I understand correctly that what I failed to do was "Exclude the Closest Server Default Rule" ?

The help states;
Select this check box if you do not want to append the default rule. The Closest Server rules feature first uses the servers specified in the rule, then proceeds to any other servers listed in the Closest Server Default rule if the specified servers are not available to the managed device. Therefore, to obtain content only from the servers specified in the rule, select this check box to exclude all other servers.

So what I'm guessing happened was the client lost communications with the local satellite and then lost communications with the primary server. So it failed to the next on the default list hierarchy which as another WAN location.