That advice comes from a Kansas licensed firearm dealer/licensed concealed carry class instructor/police officer.
Further, it would be foolish to argue that a normal individual who has just shot another person doesn’t suffer immediate physiological distress. Even police officers have to be evaluated afterward - and they are trained for the eventuality.
Finally, “I think I may be having a heart attack” is an unimpeachable statement, legally, unless you deliberately recant your assertion. “I want my lawyer” is a more impeachable statement - it can be (and has been) argued that calling for a lawyer before even talking to police is evidence of a guilty conscience.
However - everyone needs to understand the vagaries of their own state’s laws, and to use those laws as best they can to shield themselves in the unfortunate event a shooting becomes necessary.
I’m pretty certain we agree on that last point! LOL