Does ShortPixel change any metadata (title, alt text, etc)?
In short, no.
ShortPixel doesn't change any of the WordPress metadata (title, description, alt text, filename, URL and more). The only thing that ShortPixel does is to replace the original file for an optimized one.
There's also the EXIF metadata, not related to WordPress, but related to the picture itself. This contains things like where the picture was taken from, the location, what camera took it, etc. ShortPixel allows you to keep or remove such EXIF data. For more information about EXIF, please click here.