Let's be fair to the first responders. I can make many recommendations now as I am viewing the event on hindsight. Taking cover is necssary but using the ambulance is not a good choice. Running away quickly to avoid flying missiles is rational but it looks silly when no one is attacking them.
Without hindsight, I may have reacted similarly but it is ok because I am a layman. However, expectation will be different if I am in my reservist uniform as I am expected to have been trained on the appropriate action to mitigate such a situation.
Are they trained? Probably yes but was not taken seriously as such situation is so remote until that day. Are they issued with proper equipment for a riot? Probably yes again but again the second group that responded probably did not expect the situation to be so bad that they need to wear helmet with face shield to protect themselves even after getting feedback from the first responders that the situation was bad. At the end, it boils down to training and readiness.
This incident has some similarities with our mrt system. It takes a major breakdown to wake up the authority to remove the management and overhaul the system. There are many other critical systems that are working fine now. I hope that the 2 lessons are adequate wake up calls not to take things on surface value and think that everything is fine.