Hi Matt,
in my opinion the setting "Allow attendee to join meetings from a Webex node in another enterprise" is related to the Video Mesh Node (on-premises virtual machine, that terminates media to Webex). Normally the Video Mesh Node (VMN) is used on-premises to terminate media towards the enterprises Webex sites locally and thus optimise bandwidth usage. With the above setting checked, you can allow Video Mesh Nodes from other to access Webex meetings of your enterpise. In the past this had not been possible, i.e. VMNs could only be used within the own enterprise site.
Unfortunately there is not official documentation about the above setting (or at least I have not been able to find it).
Best regards
Igor