I see nothing wrong with your photo.
There two basic types of these: photos of designs under consideration used internally by those involved with the design and approval, and publicity photos like yours.
Yes, these publicity photos were regularly sent to the media, typically newspapers. They were not typically sent to individuals. Some sellers like to add the word proof or essay as a form of puffery, and granted, the design often does typically differ from the issued stamp, especially for engraved issues. In some cases, the USPOD/USPS released a photo image without a denomination when the design was unveiled, then a final photo image. The Crazy Horse stamp is an example

Size: Note the two photo sizes of the Crazy Horse photos. The Champion of Liberty photos are 3.5"x5".

I suspect the
ebay lister had a generic template for his descriptions and did not bother to measure every photo, as they vary considerably. You will want to use your photo as received and not exhibit later reproductions.
Yes, these are on photo paper. I bought one from this same dealer a month or two ago and am completely satisfied it is an original press release photo.
No, they are not listed by Scott.