This is true, sometimes. And sometimes it is not.
I was personally involved in assisting a single young black mother when her 3 year old with cerebral palsy lost her ability to eat (as doctors predicted could happen because of her motor weakness, and as the medical professionals who came to the home weekly to give her oral therapy said could happen). Mom took the girl to the ER when it happened, and the ER doc assumed that because the child was underweight (and, my guess, the mother was young, single, black, inner city, and VERY poor) that the mother was either intentionally starving or neglecting to feed her (why you'd then go to the ER, who knows?).
I went to court hearing after hearing, family reunification meeting after meeting, and heard CPS tell lie after lie, and the judge never allow testimony from the therapists who were brought into the home weekly. The case worker illegally threatened to remove all her children if she didn't immediately sign a TPR for this one. Other case workers told the judge that this mother was a threat to this child because she had a "history" with CPS (the history was, she had been a foster child raised by their own incompetent agency!).
I saw her sign a TPR because she was scared to death she'd lose *all* her children. I've known this mother for 10 years since then; she has never been on drugs or so much as touched a drop of alcohol, doesn't smoke or swear, and works full-time as a cook and has all this time.
Yes, CPS really did sever her parental rights, abruptly, despicably, frivolously, for a one-time ER visit, with many interdisciplinary layers.
It happens, a lot, to poor single young black mothers.