get_terms showing all categories instead of the ones assigned to a specific post

There are two functions:

get_terms

get_terms( string|array $args = array(), array $deprecated = '' )

Which retrieves the terms in a given taxonomy or list of taxonomies.

And…

get_the_terms

get_the_terms( int|object $post, string $taxonomy )

Which retrieves the terms of the taxonomy that are attached to the post.

You should use second one in your case, I guess…

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