You don't need to start new smarty object. This is done by XC when calling auth.php. When you do this you overwrite the already created smarty object.
Also product.tpl and any other main template will show based on what the $main variable value is. So what you have will not show your variable in product.tpl
Check this out -
https://help.x-cart.com/index.php?title=X-Cart:Generating_module_distribution_packs_for_X-Cart_4
You don't need the portion "installation" but it will show you an empty module and its way of connecting/working with the system