iPhone shares iCloud HEIC photo identified as JPEG

I had problems with a link to an iCloud photo received from another iPhone in a group Message chat that included some Android devices. I was able to view the photo on my iPhone but the Android users could not. I have read that this is not uncommon. To try to help the Android users, I downloaded the image to my phone. Right away I noticed something unusual. In the Photos app the file name was listed as "IMG0056.heic". The image type was listed as JPEG. I shared the image to Dropbox and it uploaded the file with the name "IMG0056.heic.JPEG". My Win 11 laptop was able to generate a Thumbnail for the photo but when I tried to open it with ACDSee (my photo organizer app) I got a blank image and an error message. I used a hex editor to look at the first few "magic" byes in the file and found: "00 00 00 24 66 74 79 70 68 65 69 63" which indicates a HEIF file. I removed the ".JPEG" from the file name leaving ".heic" as the extension and now ACDSee could open the photo file.

So bottom line is the photo file seemed to be an HEIC photo incorrectly identified as a JPEG file in the sharing process with the group chat. Any thoughts on what is going wrong? I realize there are ways to avoid this issue (convert the file to JPEG before sharing) but I still would like to understand why even my iPhone seemed confused about the file format.