I may be confused. Wasn't VCSO just arresting him for a crime in their jurisdiction? The thing is, if Lake Mary already had a warrant out for the murder charge, then VCSO was obligated to let them know, and Lake Mary had every right to come and take custody of him. It's done all the time.
Murder takes precedence over lesser crimes, so VCSO could not legally hold him, they had no choice but to turn him over.
I have no idea why he is bringing up that "citizen's arrest" thing... even if LE is sent outside their own jurisdiction to take custody of a prisoner, they are still LE and on police business, they're not just a citizen. And they still do a formal arrest, just to make it legal.