The site is deploying to the root of the domain, unlike when deploying on GitHub Pages. If you remove this value, all should proceed correctly i.e.
"build": "parcel build src/*.html"
Do also not that as you have a homepage key/value set in the package.json
this can result in the same issue with other tools such as React, so unless you know you need it and it isn’t an issue, I suggest removing the key and value entirely.
And remember, local testing of builds by using the appropriate build command and browsing the build output with a tool such as serve or http-server will help detect issues like this prior to deploying to Netlify.