Those are honeypot fields. They are placed there to try to fool bots into filling them out to prevent non-human browsers from validating.
Honeypot fields are invisible fields on the form. Invisible is different than hidden. Hidden is a type of field that is not displayed for editing. Bots understand hidden fields, because hidden fields often carry identifying information that has to be returned intact. Invisible fields are ordinary editable fields that have been made invisible in the browser.
The invisibility of the honeypot fields is a key way that bots reveal themselves. Because bots do not process the entirety of the HTML, CSS, and Javascript in the form, and because they do not build a visual representation of the page, and because they do not perceive the form as people do, they cannot distinguish invisible fields from visible ones. They will put data into honeypot fields because they don't know any better.
