If you read the script before piping it into your shell, you're doing better than (I'm guessing) 90% of people, but it's still possible that the attacker who got you to copy https://xn--nstall-ovf.xn--example-cl-62i.dev into your terminal has also made similarly-hard-to-spot changes to the install script. E.g. if it downloads a .deb package from https://xn--nstall-ovf.xn--example-cl-62i.dev (same Cyrillic і character in there that looks like a Latin i but isn't), you might not spot that by reading the script.

But IMHO, your "unopened bottle of ketchup" analogy doesn't work. These days, the likelihood of someone trying to trick you into running arbitrary code disguised as an install script is so much higher than the chance that someone working at the ketchup bottling plant is deliberately contaminating bottles before they go out.