I say possible because there was active shooter training scheduled today on base, so it's possible it may all be a mixup.
http://kdvr.com/2016/06/30/joint-base-andrews-placed-on-lockdown-on-report-of-active-shooter/
http://kdvr.com/2016/06/30/joint-base-andrews-placed-on-lockdown-on-report-of-active-shooter/