If the guard failed to confirm the kill of a terrorist as implied by the text, then that is indeed a bad thing. An Arab wishing to murder a Jew must allways know for certain he will end up dead, no exceptions. Also, opening fire in the presence of so many bystanders seem less optimal, as do getting your arms stolen.
26-year-old sustains serious injuries in Tel Aviv stabbing (Haaretz)
from the article: Police release security video of Jerusalem shooting attack