It's odd that the gate agent(s) didn't know how to put a passenger with an Anytime fare on the standby list. Perhaps they knew/thought there were already "too many" displaced pax or A-Listers (both have priority) that would have kept you from getting on. Glad it worked out for you.
Note: If your connecting flight is showing a significant delay, even with WGA you should qualify for no-fee standby.