My question was answered via e-mail from ACS Staff.
I'd also really like an answer to this question. Thus far my email inquiry has not been answered.
The explanation I was given is that ACS was interested in tracking any trends in changes by attendance in "government employees" in registering for / canceling attendance at an ACS national meeting. The addition of that question driven by tighter reviews of conference attendance by government employees in recent years.
I provided some feedback via e-mail regarding that question. Based on the response I received I believe ACS may consider revising that question for future national meetings.
I hope this summary if of use.