If you add Munchkin code to the Wordpress website then it only starts tracking of user activity and all the activities will be associated and pushed to Marketo lead once it gets known(i.e Fill out Marketo Form) on the Wordpress website. Hence Marketo recognizes URL as referer after Marketo form fill out.
Moreover, If you use Marketo Form embed code on the Wordpress then pre-fill functionality also does not works.
You have to use Referrer constraint for embedded forms.
Hence Marketo recognizes URL as referer after Marketo form fill out.
Not true -- a URL will be indexed for Visits Web Page filters and Web Page constraints on Filled Out Form even if it's been visited only by anonymous leads, and even if it's never hosted a form! So the URL is in fact recognized from an anonymous activity alone, i.e. it will not throw an error w/the red squiggly line. You can test this easily.
Doesn't change the fact that the Referrer constraint should be used for Filled Out Form w/embedded forms, because it allows for accurate pattern matching