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