That description sounds to me more like a witness to the shooting who was hit with body material.
The shooting took place at the drydock, where the sailor was on duty and the civilian shipyard workers were . . . working. The “nearly naked” man was just outside the base, near the entry gates, an obvious civilian. My suspicion is that he was somehow involved with or known to the shooter, Gabriel Romero, but he was nowhere near the shooting. He may have had a nasty argument / breakup with Romero earlier in the day and followed him to the shipyard, distraught and suspecting something nasty was going to go down.