Using the zip option to upload your components is the easiest way but it comes with a responsibility. Playground platform becomes blind with zip files & doesn't run any validations thus, solely trusting the user's capabilities.
As a thumb rule, if you are able to see src or force-app folders in root on your Components section on the Play Detail page, Playground will always pick them & run your deployments.
To make it right with the zip upload option, place your src or force-app folder into another folder. Let's call it a parent folder and then make a zip out of this parent folder rather than zipping src or force-app folders individually.