Hey man, let's finish this? lack a little!
Well was missing the letter "n" in the spelling of the variable "nonAdmin" in some places. I fix it and work.
Now the thumbnail is being displayed, the title and date also are displayed correctly.
Isn't correctly displayed the name of the author.
And permanlink is pointing to the wrong place.
The code is above:
$nonAdminPosts = get_posts(array('author' => -1));
foreach($nonAdminPosts as $nonAdmin):
<li><a href=" ">$nonAdmin->post_title</a></li>
echo get_the_post_thumbnail( $nonAdmin->ID, 'thumb-size' );
the_author_meta( 'user_nicename', $nonAdmin->ID );