First of all, the intention of the people jumping off of the building was not to die. They were trying to survive.
Attempting to climb down was by far the right decision as the chances of survival are higher.
O you who have believed, do not consume one another's wealth unjustly but only [in lawful] business by mutual consent. And do not kill yourselves [or one another]. Indeed, Allah is to you ever Merciful.
Quran, 4:29, Sahih International
From this meaning we can see that you cannot kill yourself.
I believe that it is merely a personal choice in time of emergency when their intention is not to kill themselves. This is because every mind will act differently. The number one thing you need to keep in mind is that you are not intentionally trying to kill yourself. You cannot be 100% certain you are going to die if you jump off. Usually, police officers/firefighter will have trampoline like objects around the building in case of fire in order to save them. Those who jumped might have thought this was the case.
For example, if you are in that situation and have two options either to jump or to do nothing, I would first recommend you to make dua and ask for Allah to help you make the right decision. Some people will freeze and be in shock when this happens forcing them to do nothing. If the fire was all around you and you are backed against the window, the less risky option would be to get out through the window. On the other hand if you were to be on the stairs then the better option would be to run down the stairs. But none of these option are directly related to suicide. Hope you understand. There are a lot more factors in what decision the person makes but the person is ultimately trying to save him/her self. This should not be a problem in the case of Islam. If it was obvious that the method he/she was taking is destined death, ex. going into space without a spacesuit without doing preliminary testing on the effects it will have on the human body, that would be haram as it is related to your lack of knowledge.
And spend in the way of Allah and do not throw [yourselves] with your [own] hands into destruction [by refraining]. And do good; indeed, Allah loves the doers of good.
Quran, 2:195, Sahih International
This clearly says that you cannot put yourself up to be harmed/destroyed. More importantly you cannot let harm come to you and just be still. Therefore remaining still and not doing anything would be more discouraged as that is letting yourself come to destruction by refraining.