The SG-1100 does not have an RTC battery. pfSense will bootstrap the system clock at boot from a number of sources, whatever is most recent. Here it would have been the last filesystem time stamp. Once it has a WAN connection it will update using ntp.
That doesn't explain why it was asking you to assign interfaces though. That would normally only happen if an assigned interface is no longer present. If you had used a USB Etherner device and then disconnected it for example.
Steve