Yeah that story is full of holes.
A) Potassium isn't injected, it's administered as a slow infusion, usually over 2 hours/10mEq. Rapid infusion will render the heart unable to beat. Also, it's a very acidic solution and is caustic to the veins when administered at a rapid rate.
B) Hypovolemia can present with high or low potassium, so no Dr with half a brain would assume that a hypovolemic patient is hypokalemic. Nobody would ever assume the potassium level of ANY patient simply because it's such a critical electrolyte
C) A hyperkalemic patient will have an EKG that is immediately recognizable and totally different than a patient with low potassium. No mistaking the two.
D) Again, a patient who is fluid-depleted will be treated with isotonic fluids. Not potassium (assuming bloodwork doesn't reveal any major type of deficiency).
Was it possible that this doctor was intoxicated and committed grave medical malpractice? Sure, but as Sarcev admits, the only other person in the room was Thierry Pastel. So this is a third-hand account, witnessed by someone with little medical knowledge, ie: the whole story is suspect.
To me, it's more likely that Sarcev's telling of the story is inaccurate. But if you want to believe that the medical staff at the hospital committed a series of serious, basic errors that would probably result in the revocation of the licenses of everyone involved, go ahead.
