[wildbill]

If this is only part of an even bigger meteor that 'cracked' apart as it went through the atmosphere, then where are the other pieces and why does this impact crater look round in shape?

[ZGuy]

Think in terms of a shotgun blast at close range into the dirt. Lots of indiviual pieces of shot, but it would leave one "crater" -- not 400 little craterlets.

Now add in tremendous friction due to high speed. So much so that the pieces of shot break up into dust sized fragments and form what the article calls a "cloud" -- same speed, same mass, just not big chunks, hitting the ground. That's basically the theory.