As promised I made some time to list a few things.
First of all like someone already commented on youtube, not everybody died immediately, and there were warnings there's a bunch of people who got away. Those who died were those who stayed behind and were confident that nothing serious would happen.
Another point is the statues, the death did not turn into stone. Thing is, when archaeologist discovered the site, they realised that there were "holes" in the solified magma where people used to be. Their bodys mostly decomposed, but the space that they took up left open under the ground due to the structure of magma. Then they filled those "holes" with some sort of plaster, to reconstruct the position of the people, and then after digging them out they carved the plaster "blocks" and added facial expressions and the like to make it more impressive to tourists.