Hardcoded database creds in code. Saw a post earlier with credentials to an rds instance. It said there were more examples.
EDIT Found it again: https://sizeof.cat/post/twitch-leaks/#secrets-exposed
EDIT Found it again: https://sizeof.cat/post/twitch-leaks/#secrets-exposed
The site you linked to detects if the referrer url is HN and instead displays only an image saying "HACKER NEWS - A DDoS MADE OF FINANCE-OBSESSED MAN-CHILDREN AND BROGRAMMERS" instead of the content you are trying to link too.
OK Then...