Can anyone help me out on this image? Can't remember what I did.

So, I modified this image as a raster file and of course I didn't save as .psd after completing it, so I have no way to check the action history.

You might be misunderstanding, the History is not being saved with a file (except as a History Log if the Preferences are set accordingly), non-destructive image editing in Photoshop depends on the use of Layers, Adjustment Layers, Smart Filters, …

If you did not use those anyway the psd would not provide meaningful clues and you may want to overthink your image editing process completely.

Certain details of the b/w image and the color version seem to differ so much that it seems likely the new file is noticeably different from what you started with originally anyway.

Black & White or Channel Mixer Adjustment Layers can be used to make the Smart Object neutral and as the previous poster mentioned the Layer Style »Outer Glow« was likely involved.

I think if you are converting it to Grayscale, then the yellow Iris is to dark.

Then I would imagine you gave it some sort of outer glow as well.