I got an engineering degree and probably worked on my car underneath it using only a jack to hold it up. Now that I’m older and wiser I use decent jack stands and put the tires underneath the car too as a second chance. I always gave the car a good shake in all directions to confirm it was steady, and always used blocks or rocks under any wheels that were touching the ground.
So sad to hear of this accident.
I did the same thing back in the day but wouldn’t think of doing it now. Funny how your perception of risk changes as you get older. Just the thought of being under a car with just a jack gives me the willies now.