Can my flutter developer crash my site without access to my website or database

So I hired a flutter developer who was supposed to create an app for my Wordpress site.

This guy went MIA and all of a sudden after 3 weeks he is asking for money for work he hasn’t done.
So I clearly told him that I won’t pay as you haven’t done any work nor submitted anything.

Next thing I know my website is acting funny and now it says database connection not established.

The only access he had to my site was to the wp-admin

I hadn’t shared server or cpanel or database access.

Can he do something to crash my website from the app that he had connected to my site?