“Killed in action” (on the mural) or “active service” (on the plaque) often means killed by a bomb exploding prematurely, as in the case of Finbarr McKenna, who died in Crocus Street intending to attack the RUC station on the Springfield Road at Violet Street. Here is an account of McKenna’s death from a British soldier. Lost Lives estimates that as many as 163 volunteers (9% of the total killed by the IRA) died from premature explosions. Footage of McKenna’s funeral appears in the (Sinn Féin-produced) account of Larry Marley’s funeral.
The plaque dates back to at least 2004.
Click to enlarge (to 1400 x 2034)
Copyright © 2018 Extramural Activity
Camera Settings: f4.5, 1/200, ISO 80, full size 3469 x 5039
text: X04992 In memory of IRA Volunteer Finbarr McKenna who died on active service in Crocus St. 2nd May 1987. Erected by the Greater Clonard Ex-Prisoners Association.
Extramural Activity 
The soldier’s version of the events surrounding Finbarr McKenna’s death, which you have linked, are largely fabricated. He did not suffer the kinds of injuries described, and the accounts of the actions of dogs are, therefore, impossible. I know because I was on the scene in its aftermath.