In the Google SRE book they say that if a service has reliability much better than the stated SLO they artificially introduce errors to get closer to the error budget.
This is to prevent over-reliance on the measured SLO rather than the stated SLO in upstream services.
My understanding is that they don't bring the service to exactly the SLO... To prevent overreliance on a service, it can be sufficient to introduce some level of failure, which may still be well above the SLO.
One major issue and you stop artificially inserting errors, which are inserted at a rate such that you could turn off the error inserted within some timely manner and still stay within budget.
I think you'll find neither story is true.
Like most Urban Legends it's a bit silly, people are people whatever the culture. They have common sense.