Alluding to this spoiler ahead of time is definitely not ideal, especially considering that for many people, the death of the young hero is the knockout blow after a series of emotional gut punches at the end of the film as Thanos snaps his fingers and wipes out half our heroes and the universe.
This is wild because the host of the screening even warns the audience ahead of time about not spoiling the film for people seeing it after them.
Tom Holland really is a fan though, and he just seems to get so excited about his role, the MCU and the fandom that he forgets to stay buttoned up.
Also given his penchant for letting cats out of bags, he probably should have been told before coming onstage whether or not the audience had seen the film yet.