Read the article so you don't have to:
Unlike the title suggests, the docker images they found won't leak your credentials when you use them, but already contain the credentials of whoever created the image (p.e. through .env files that were accidentally added to the image).
While it contains the valuable reminder to avoid long lived credentials (like API - keys) or use secrets-stores, this "leak" is on the same level as accidentally pushing confidential information to github IMHO.
Fix: have both .gitignore and .dockerignore files and make sure they both contain .env. You use .env and don't hardcode your secrets, right?