This is true if you look specifically at January 6th, no police officers died that day. Initially the story was that Brian Sicknick died after being beaten by protesters, or mors specifically a fire extinguisher.
While in the video it supposedly shows Brian Sicknick walking around after he was supposed to have been beaten to death.
According to CBS, "Despite being sprayed with a chemical substance, Sicknick's manner of death was determined to be "natural," the medical examiner's office said. In the interview with the Post, Diaz said the autopsy found no evidence of internal or external injuries, or of an allergic reaction to the chemical substance — but did say "all that transpired played a role in his condition.""
They further go on to say, "The "natural" classification is used "when a disease alone causes death," the medical examiner's office said in the summary. "If death is hastened by an injury, the manner of death is not considered natural.""
CNN does say, "The DC medical examiner ruled that he died of natural causes but said, “all that transpired (on January 6) played a role in his condition.”"
But as we see in the quote from CBS, "if death is hastened by inury it's not ruled natural," but Sicknick's death was deemed due to natural causes.
From all the information I've found in these sources and others, this does appear to be true. If this was done unintentionally than that could be a reason. There were 5 people who died that day, but none of them were police officers.