the_ID()
prints the current post’s ID. You need to use get_the_ID()
to return it.
Also, get_the_category
returns an array of category objects – one foreach category term the post belongs to.
The ‘category’ attribute expects a category term ID. So you need to pick a category object, then obtain its ID:
$cats = get_the_category();
$cat_obj = array_shift($cats);
$cat_id = (int) $cat_obj->cat_ID;
Then:
$args = array( 'numberposts' => 5, 'offset'=> 1, 'category' => $cat_id );