Look in the assets/snippets/weblogin/ folder and find the file named
weblogin.inc.php, this is where the default weblogin templates comes from... it starts near the bottom of the file in this section:
# Returns Default WebLogin tpl
function getWebLogintpl(){code here}
The chunk.weblogin.tpl file is an example file with code you can use to create your own chunk in the MODx manager and then call it in the snippet if you desire, but its not required and is not called by any of the weblogin functions.
And just FYI, the weblogin template code is table based