You notice that new records in Marketo have the 'Website' and 'Company Name' fields populated with the domain of their email address.
This will happened when a new lead is created by a form fill-out. If the new record is imported or created manually then this would not apply.
This design decision has been a part of the code for many years where the domain of the email is used for the company name and website fields on the lead record. This feature cannot be disabled.