Gents,
The crossed cannons on the flag of Austin's battalion (the 12 star Mobile Depot made Second National) have nothing to do with being associated with the 5th Co. Washington Artillery. These were CSA Western Theater only battle honors for the capture of Federal artillery in battle - so at some point Austin's Battalion captured Federal guns. I have the general order for this honor in my files.
As to why the flag was in Columbus when the bulk of the battalion were in Mobile, I can only surmise that at some point the unit passed through Columbus (did they go into Tennessee with Hood?) and maybe left their flag behind.
The hospital scenario is a possibility as well.
Greg Biggs