Wordpress - Correct use of get_the_terms()

the_ID() print the post ID. You need to use the get_the_ID() which return the post ID.

Example:

foreach (get_the_terms(get_the_ID(), 'taxonomy') as $cat) {
   echo $cat->name;
}

Always remember the naming convention of WordPress for template tags. the which mean to print get which mean to return in most of the cases.