This illustrates the difference between common parlance and technical use of words. In this case we have:
- everyday understanding of "dead"
- legal definition of "dead"
- medical definition of "dead"
Let's go backwards up the ladder. If they're trying to resuscitate him (regardless of DNR), medically, they don't think he's dead. The technical term (in my research realm) is "catastrophic organ failure", which after time (depending on which organs and how failed) will lead to death. But is not death.
The legal definition, in most jurisdictions where I work, is tied to a "competent medical authority" declaring death. So, after society selects who is "competent", the legal and medical definitions become one in the same.
[DIGRESSION ALERT – On active duty in the USN, certain cargo movement operations require, by law, that a "competent person" be in line of sight and conduct supervision of activities. That requires specific safety officer training, after which, I received an id card that named me as a "Competent Person". I still have it … but … it is past its expiration date.]
So he met neither definition of "dead".
In the conversational sense in the 21st century, that standard is pretty much the same as the others. It's heavily influenced by fiction media where we see people "brought back" by technology. So in the modern zeitgeist, if you said someone was "brought back from the dead", most people would reply "They weren't really dead." Interestingly this attitude is the ancestor of the "three days" standard of old where you weren't really dead until you were dead for three days (which interestingly aligns with the time you can go without water).
Three strikes, and he's not out!