No, it’s almost unthinkable. The one time a gun actually does go off in Legend it’s fairly unmistakable, and if we assume there would be multiple gunshots (as there would have to be for there to be two victims), it becomes increasingly unlikely.
“They weren’t paying attention” isn’t a good enough explanation for me to swallow. I’d want more textual support as to why they wouldn’t pay attention, or why it wouldn’t be reasonable for them to have heard anything considering they later do hear something just fine (admittedly from a closer point, but they’re still many rooms away with at least one obstruction between them and the source of the sound).
More likely is there were no gunshots.
EDIT: Also just to dovetail Karifean’s stuff and not to rip him or indeed basically anyone who likes doing this, but what makes people so sure that “Yasu” exists as a character in Yasu’s own stories? I find it particularly unfair when people say things like “Dammit, Battler, you’re so dense” when discussing a fake, fictional Battler written by the very person you’re supposed to sympathize with who is also the avatar of the author of the story. Like no shit Battler is dense if Yasu’s sole expectation was that he didn’t remember, but that isn’t real; it’s Character-Battler interacting with Character-Shannon/Kanon/Beatrice, and I don’t think we can say there is a 1:1 correspondence between the two (moreso with Battler obviously, since one presumes the author knows more about her own creations than another real person).
People have a distressing tendency to ignore that this is in-universe fiction (double super-secret mega emphasis on fiction) and I worry it allows them to be manipulated to certain conclusions that alter perception of the story as a whole. Like wow Yasu’s personal characters are sympathetic in a story she herself wrote, no really, fascinating.
Again not trying to rip people on it, it’s not an invalid reading, but I feel as though it is incomplete unless we understand the greater emotional tragedy here, that Yasu’s expectations for Battler were so low pre-incident that she had essentially no faith in his ability to figure out what was really going on; expectations, I would note, that were more likely than not confounded by whatever “true” Battler actually did show up (to such extent as we know him from Tohya and the boat scene in EP8).