Custom Theme Showing Update Available, Not Possible

So this is a very strange situation and after extensive searches I could not find anyone else with this problem.

I manage a WordPress website for a client and I created a custom theme for them. It is version 1.0 and I have only ever updated the theme by FTP. I logged into the WP admin today to update something on the site and saw there was an update so I went to the updates section.

It said there was an update available for my custom theme. It said “You have version 1.0 installed. Update to 2.5.8.”

I know for a fact I’ve never made an update for it and it definitely wouldn’t be 2.5.8 if I had done so. My thought is that somehow someone stole my theme and made a public version of it with malicious code. Is this possible? Has anyone else experienced something like this?

The site is viewable at https://hopechristianfellowship.org/ but obviously there is nothing really to see on the site itself. It’s a backend situation.