You need to know what the number show are. They may not be file size. Here in image size you see several numbers. Lets start with dimensions 420px x 624px How big is that? It depends. You can see it is a color image most likely RGB it could be 8 Bit color or 16bit color or 32 bit color in Photoshop. In 8 bit color for each pixels there are 8bit for Red and green and blue so 3 bytes per pixel in memory the are 420x624x3=786,240 bytes 8bit color 1,572,480. If you look at the top of the Image size dialog you see an image size number 767.8K which is hex 1K hex 1024 bytes it you divide 786,240 by 1024 the resulting hex number is 767.8K so the Image size numbers all make sense for a 8bit RGB image. If the image is saved in Jpeg format the pixel data will be compressed and the amount of pixel data will be less the 767.8K much less if you save in low quality.
Next you show a Jpeg Option dialog and there is a number 7.3M the is no label on the number. If you save the Jpeg and the file size turns out to be 7.3MB file I would think you have over 7MB of ancestor Metadata you can strip.
I've been using this template for months.
Templates can build up excessive amounts of photoshop:DocumentAncestors metadata if you save over them each time… So I agree with JJMack, it does indeed sound like: