WooCommerce is_product_category() not working

by

is_product_category() – Check If Current Page is a Product Category

Try this

add_action( 'woocommerce_single_product_summary', 'product_short_description_by_category', 20 );

function product_short_description_by_category() { 

        if( has_term( 'cake-toppers', 'product_cat' )){ 

                echo 'A cake topper'; 
        } else{ 
                echo 'NOT CAKE TOPPER'; 
        } 
}