What's the Difference between Convolution Kernel and Point Spread Function in the Context of Image Convolution?
The PSF (Point Spread Function) is the system response to Impulse Signal (Point).

If your system model is LSI (Linear Spatially Invariant) then the output image of the system is applying the PSF as a convolution kernel on the input image.  

Yet, the PSF is just the response of a system to a certain input.
It doesn't describe the whole system unless it is an LSI system.

If you model for the Deconvolution problem (Often called the Degradation Model) is LSI, then what you estimate is indeed the PSF.