list taxonomies from a custom post type

In your code you’re using this to register taxonomy:

register_taxonomy( 'events_category', array( 'events' ), $args );

So the taxonomy is called events_category.

And in get_terms you use events_categories.

Here’s the fixed getting terms part:

$terms = get_terms( array(
    'taxonomy' => 'events_category',
    'hide_empty' => false
) );