First - it was not a fuel injected car
If it's the 4.3L V6, yes it has throttle body fuel injection which is not as fuel economical as multi-port injection but otherwise does still have the computer, measures airflow and temperature and doesn't have the choke issues of older vehicles. They start and run fine cold. Then again, vehicles I had before the one with a 4.3L V6, with carbs, also started and ran fine within a couple minutes. It is not really relevant to the discussion when talking about more than a couple minutes in weather that's not arctic cold.
Second - the auto manufacturers have designed warming up into most every car, which they call remote start. If the manufacturers designed it into the car, obviously it is OK.
Not at all. Being able to remote start a car doesn't make it legal or morally acceptable to do so even if it is running well which it seems not to be if the exhaust is this noticeable.
There are laws in many areas about not leaving a car idling unattended. Where Muse is in CA the legal limit is 5 minutes. That it's a feature from the factory doesn't change that. Most vehicles with factory remote start also turn themselves off after a period of time like 10 to 15 minutes. Maybe that time limit is reprogrammable but either way, illegal for 1/2 hour.
Most vehicles can also exceed 80MPH and that's
usually not legal either. They'll go into gear without the seatbelt being used, also not legal in most areas. It's also not legal to circumvent emissions control devices in most areas, nor excessively pollute either way even if the vehicle is not subject to emissions testing on a routine basis unless it falls under a classic car exemption.
If it were a modern vehicle in good running order, so it idles quiet with minimal exhaust fumes, it might not even be noticeable outside.