‘get_previous_post’ in same category returning (!empty) when no previous post in category exists

Figured it out 🙂 It ends up the Smarter Navigation plugin has a few other functions that I missed:

https://plugins.trac.wordpress.org/browser/smarter-navigation/trunk/template-tags.php

I used get_adjacent_id_smart() like so:

<?php
    $prev_post = get_adjacent_id_smart(true);
    if(!empty($prev_post)):
        echo 'not empty'; 
        previous_post_smart();
    else:
        echo 'empty';
    endif; 
?>

And I got the behavior I was looking for, don’t know why the default WP function was not working according to the codex.