Why is the form prefilling user's data?

I send the form out to customers and they couldn't get pass the 1st page.

This didn't happen ever when we played with it in house. We published it by emailing the link to each customer.

When I went in to problem solve... I did a preview and the autofill data is now visible when I published the form... but I didn't have any problem getting past the first page.  

Question: I am not currently concerned about the inability to get past 1st page, but how do I get the form to clear out the autofill from the "preview" data??

In the meantime I disabled the form.

Your form has actually the autofill feature enabled, please find more  details about this information here: https://www.jotform.com/help/227-How-to-Enable-Auto-Fill-on-Forms 

I would recommend you to test your form using incognito mode and see if the same happens, the data is stored in the browsers cache and it's cleared when you either submit the form, clear the browsers cache or after 24 hours if it's not submitted. 

If you still experience the issue, please kindly share us some images about it, since attached images via email replies will not be posted here, you will need to follow this guide instead to upload your images: https://www.jotform.com/help/438-How-to-Post-Screenshots-to-Our-Support-Forum 

Thanks.