What does Trump mean that the U.S. has one of the lowest covid mortality rates?

Can you cite any of this crap?

In other words, he is spewing bullshit:

On Bullshit is a 2005 book (originally a 1986 essay) by philosopher Harry G. Frankfurt which presents a theory of bullshit that defines the concept and analyzes the applications of bullshit in the context of communication. Frankfurt determines that bullshit is speech intended to persuade without regard for truth. The liar cares about the truth and attempts to hide it; the bullshitter doesn’t care if what they say is true or false, but rather only cares whether their listener is persuaded.

With good reason in that case. The more they look, the more it appears that this coronavirus is more of an infection of the cardiovascular system, rather than just of the lungs. So it can cause strokes, heart attacks and other bad things. Here’s a cite, if you want one:

It should be noted that this is also standard practice for measuring deaths from infectious diseases.
e.g. Someone is admitted to hospital with the flu and they test positive for a strain which is known to be potentially deadly. They are also found to have a severe issue with their kidneys and soon their kidneys shut down and they die apparently from this latter ailment.

AIUI the cause of death will likely mention the flu, and their death will be counted among the flu deaths for that season. It’s just simpler to do it that way, and while on the individual level this might be misleading, from the epidemiologists’ point of view over many thousands of cases, it’s a relatively small source of noise.
It’s not a special new rule for covid.