The value of $file['meta'] is a string, not an array. That means your approach to access the value does not work.
It looks like that meta value string is a json encoded object. If so you can decode it and then access the property "name" of the resulting object.
Take a look at this example:
<?php $file = [ 'uid' => '52', 'guarantee_id' => '1116', 'file_id' => '8', 'file_category' => 'test', 'meta' =>'{"name":"IMAG0161.jpg","type":"image\/jpeg","tmp_name":"\/tmp\/phpzdiaXV","error":0,"size":1749244}', 'FileStorage' => [] ]; $fileMeta = json_decode($file['meta']); var_dump($fileMeta->name);
The output obviously is:
string(12) "IMAG0161.jpg"
In newer version of PHP you can simplify this: you do not have to store the decoded object in an explicit variable but can directly access the property:
json_decode($file['meta'])->name
The output of this obviously is the same as above.
$file['meta']is a string, not an array.