The problem is that your theme still load the main style.css sheet, because it is called by wp_head()
. See the documentation here
So, in order to not load your theme main stylesheet, you have to add to your functions.php
file :
add_action( 'wp_enqueue_scripts', 'yolo_my_custom_template' );
function yolo_my_custom_template(){
if ( is_page_template( 'name_of_your_page_template.php' ) ) :
wp_deregister_script('twentynineteen-style');
wp_deregister_script('twentynineteen-print-style');
endif;
}