Hi Flowe,
The code that WooThemes has supplied you is for their Product Vendor plugin. Not WC Vendors. 🙂 You don’t need to do *anything* with WC Vendors, other than simply install Product Enquiry. We automatically detect it and route the emails to the vendor for vendor owned products. It’s as simple as it gets! 🙂 You should delete that functions.php code snippet entirely. 🙂
Cheers,
Ben