"Realist" my arse. That shit was abandoned ages ago. He literally invoked the fuckin power of friendship. Given that bullshit social propaganda gets peddled by almost every Japanese series ever, despite being completely contrary to the real-life norm, it is probably about as far from realism as you can get.
And in classic isekai fashion, he didn't even consider for a moment that people in a world like this might not be used to fireworks. Seriously, if you were used to random outbursts of war and had never seen fireworks before, you'd probably think the city was under attack. He didn't even consider that for a second.