I don’t know anything much about Home Assistant but the link @jkp posted talks of installing a SmartApp on SmartThings with the aid of a PAT and what you would appear to have there is an installed instance of a Webhook SmartApp.
The actual code of the app will be at the Home Assistant end. Clicking on that tile just causes SmartThings to interact with that app over a Webhook URL to update its configuration and authorise it to do whatever it is doing.
Webhook SmartApps are pretty boring in the SmartThings app because none of the interesting stuff they can do with dashboard cards like you can see with the stock apps is documented.
I’m a tad surprised to see it in the Routines page and not hidden away on the Linked Services page.