One presumably talks about the production environment, the other about staging environment.
- Very strict coding guidelines
- Rigorous code review
- An extremely thorough test suite
- Multi-stage approval through a QA process involving many pairs of eyes and thorough, formally defined and scientifically rigorous test procedures
- Static analysis and possibly even algorithms proved correct in Coq
Simply playing with it in staging for a while and determining that everything looks good is NOT the kind of testing that you do when there's "no room for error."
These are substantially higher bars than "play with it for a while and see if you can break anything."
Staging = "ready to roll", not "still needs testing to see if things break". Things shouldn't break on staging.
Of course you can forgo manual QA if your automated testing is so perfect that staging is just a formality. I'm guessing ZenPayroll has that covered, given that they deploy to production "several times a week".
So I assume "trying their best to break things" is just a flippant description of final acceptance, not QA testing.