Jpeg replaced by rogue Alias file

Mac OSX Mojave. I was looking through old photos in my Lightroom catalogue the other day, when I noticed that one was marked with a little black circle and an exclamation mark "lightroom has encountered problems reading this photo". The photo in question was a scan I did (one of a few thousand) of a slide, back in 2011. If I show the file in Finder, I see that the file is not a jpeg at all. It used to be, and is still named as it was (img_r_0394.jpg), but it is now a 904 byte Alias file. The alias is pointing to /Library/Application Support/Adobe/Uninstall/ACR_11_1.app. The date of the alias is 12 Dec 2018, so I thought this won't be a problem because I have an off-site backup from before then. However, the rogue alias is present even on the older backup, but this time it is pointing to /Library/Application Support/Adobe/Uninstall/ACR_10_5.app and is dated 26 Aug 2018.

Fortunately I still have access to my slides, so I can scan it again. However, how could this have happened?