Duplicate lead filled out "web form"

A "Potential Duplicate Lead" alert was brought to my attention. When searching for the lead in Marketo, I saw it appeared six times in our database, it had a company of "google" and that the lead entered Marketo through filling out a "web form" that isn't a Marketo form. What could be an explanation for this lead appearing? And what would that extraneous "web form" be?

Thanks, all!