Nope, my southbound MARC train was also impacted.
South of the station, VRE tweeted that their trains were being held as well.
Overall, a minor hiccup. The train I was on pulled up behind the MARC train in front of us on the platform at NCR (thankfully a veeeeeery long one). We were advised that it may be a while and that Metro was honoring tickets. I hung loose on the platform for a few minutes, and was rewarded when the first MARC train left, and the conductors shouted that we were going to move as well and welcomed us back aboard. The small handful of us had a slow, but uneventful trip in, arriving at WAS maybe 30 minutes later than scheduled.