If you set the Outer Glow style to the "Precise" technique it also shows direct evidence of a canonical distance transform. But what is the algorithm used for the "Soft" technique? It does not look like a distance transform. At least, not directly. There seems to be some sort of blur. But its not a blur because I try blurring the mask using similar settings, and doing a difference calculation on the outer glow versus my blurred mask.
