What’s the snippet call you’re using? Are you using the &thankyou=`(id)` or &goto=`(id)` parameter? They work quite differently.
&thankyou will display content inline. It works with chunks, snippets or indeed a document (extracting the document content). The advantage is here that you can use eform placeholders to display any of the form values.
&gotoid simply redirects/forwards to the document given. This is what you expected yes? The disadvantage is that there is no access to any form values.