It was a terrorist attack on civilians. That's a tragedy no matter the surrounding context.
The surrounding context can give a different perspective on a tragedy, though. In the context of nurturing the conditions that produced 9/11, creating a civic religion around it, doing horrific war crimes as a response for the past 20 years, and then sweeping under the rug that month during the pandemic where we had a 9/11 every day, I find that humor is the best way to communicate "shit's crazy, man."
Some thoughts on this from the 9/11 megathread. My comment (objectively the most correct take):