Maybe because the structure wasn’t completely set yet, so when I poured the sour cream on top it weighed down and the part that wasn’t set “collapsed”?
Cracks form more easily in things that are brittle, rather than soft, which is why hitting a glass jar will shatter it, but will only dent a metal can, or at worst, a small hole. Most metals are not brittle.
It is possible, though, your crack isn’t a crack, but a separation of two layers, but it does look like a crack and the fact that it begins at what looks to be an air pocket is suggestive. An oddly shaped air pocket could produce a stress concentration at a point where there is a sharp corner like the window of the Comet.
A big temperature gradient within an object can produce stress (drop a frozen glass jar into a pot of hot water), so I agree that putting it in the refrigerator warm might have been part of the contributing cause.
If that is an air pocket on the left, then a firm rap of the pan on the counter might have eliminated it and gotten rid of the stress concentration that led to the crack. I believe that many cheese cake recipes recommend that procedure, do they not?