You complete the entire spell before performing any relevant triggers in the queue. So we deal 3 damage to Stewardess, killing it (and adding Dies: Draw a card to the queue), then I discard a card because shadow blade killed the patroller.
Having now completely finished casting shadow blade, we look at the queue for the next thing to do and we see we have a “Draw a card” in there from the technician death.
If you want more detail, its been asked and explained many times in the rules thread, but here is a good explanation to why this happens Rules Questions thread - #1039 by sharpobject