Hi Jodie,
Marketo calls all record Leads. In Salesforce they can be either a Lead or a Contact. So if Marketo is telling you that it's a Lead, it may actually be a Lead or a Contact in SFDC. You can use the field "SFDC Type" to differentiate between Contacts and Leads. That field will be populated in Marketo as Lead if it is a Lead in SFDC and will be populated with Contact if it is a Contact in SFDC.