Adding a column to search results
Unfortunately you can't use searchColumns to add column on contact search result. The layout in tpl doesn't respect the 'searchColumns' hook.

However you can still use the hook by doing some additional UI setting or using javascript. Here are some alternate approaches


Create a profile with same column as Find contact and set 'Visibility' to 'Expose publicly and for listings' and Results Column? to true for each field. Navigate to CiviCRM >> Administer >> Customize Data and Screens >> Search Preferences. Use the created profile as 'Default Contact Search Profile' option. Alter the code accordingly to adjust the result display.
Add javascript to insert a column(td) for each row(tr) against each contact using the contact id defined in id or class for tr element. Iterate based on $rows assigned to tpl.


HTH

Pradeep