That was my first thought. Why did they evacuate out of the rear right slides? They must have had a reason. I used all 4 slides one day with a bomb threat and our Chief Pilot questioned why me, a new captain, elected to use all 4 slides when the bomb was set for 2500 ft. I said because they are not FAA approved bombs and the altimiters are old and could stick unless you wait for them to go off. Besides, I asked for push up stairs so we didn't have to use the slides but with 10 minutes advance notice on downwind at LAX nobody got us any. Never heard another word.