I think that this is a risky idiom. Read without context, it simply means that someone is considered to have done adequate work having done lesser work, or have behaved adequately when they otherwise would have not had they been someone else.
The phrase, "held to a lower standard", however, is a play on "held to a higher standard", which is often used as a kind of compliment. For example:
As a teacher, you are held to a higher standard of ethical public behavior than most other people. For example, even if most people break the law and smoke marijuana, you, as a teacher, should not.
So, the phrase "held to a lower standard" is a play on words, a kind of joke, and even an insult.
Additionally, the somewhat unstated ethos in the United States is that everyone should be treated equally, and that equal standards should be applied whenever possible. Thus, any exception to this is suspect, and requires explanation.
Moreover, many people would say that, if a person didn't have an "equal opportunity" (another politically loaded idiom), that the responsibility to help equalize the situation falls, not only on the individual, but society at large.