I don't know whether this guard acted rightly or wrongly. The trouble is that there is a widespread perception both among Palestinians and across the world in general that Israeli guards and soldiers hardly ever get punished for shooting Arabs whatever the situation. That's why Arabs tend to react by taking the law into their own hands because they don't think they'll get justice from Israel.
Swedish police arrest man in Stockholm area on suspicion of preparing terror crimes (AP)
from the article: Israel Police leave Temple Mount as calm returns to Jerusalem