It's essay time people! And we're diving into this glorious scene-
When I say there's no fillers in this show, I really mean it. So what exactly is the importance of this tiny clip of White talking to a random guy we'll likely never see again, you might ask. Well there's three levels of significance here and I'm gonna break down all three. Because I can and it's fun!
The first level comes in the form of the guy using whitener on the shirt to make the ink less noticeable. He says "that'll do it for now" as he does. This scene is symbolic of how the authorities, when faced with glaring issues, would rather just cover them up instead of properly fixing them. The problem doesn't go away, it simply becomes less noticeable. This part is pretty self explanatory and has been pointed out by a lot of people already so I don't think we need to go into much more detail here.
So we jump to the next level of significance, i.e., White getting an outsider's perspective on the fire-
In this scene when the man supports the arson, even if it's not fully, it shocks White. He was firmly against it because he holds the law as paramount. He thinks that Black and Co's attack going against the law invalidates whatever good they may be trying to do. But here's a man in the exact same position as White who is actively agreeing that what they did brought positive change and it forces White to acknowledge that their actions are not totally negative and harmful and that there is a flip side to the debate. There's also this-
The acknowledgement that, while their actions are in good faith, they still committed an illegal act and, at the end of the day, that will bring legal repercussions their way. We can all agree that what they did made a positive impact but that doesn't mean they are exempt from the law and if caught they will face legal repercussions the same as anyone else. This solidifies their status as vigilantes. They're not heroes, they're just men with a need for justice who are willing to go to some extreme lengths to get it. But they're not villains either. They exist in a grey area and trying to judge them from a hard-set, black and white perspective like White has been trying to do just doesn't work.
And that brings us to, in my opinion, the most important dialogue in this whole scene-
The very blatant acknowledgement that people in positions of power will actively deny the positive impact of such acts and look the other way when such injustices occur, simply bc of the positions they hold. Having opinions that go against the Powers That Be is a luxury people in these diplomatic positions simply aren't allowed and if White joins the ministry like his father wants him to then he would have to actively condemn his brother and his gang. Irrespective of whether what they did had a positive impact and/or whether White himself agrees with their actions, he will not be allowed to exist as a government official while taking the side of the people.
I think this scene foreshadows an important decision White will have to make in the future, where he has to choose between his father and his brother. Will he stick to his ideologies, hold the law paramount and look the other way when people in positions of power abuse the legal framework to take what they want? Or will he finally let go of his idealistic perspective and take Black and Co's side in their fight against the corrupt authorities?
So that's three levels of significance: pointing out how the authorities cover up issues instead of putting in the effort to fix things, forcing White to acknowledge that what Black and Co are doing is far from black and white and he cannot condemn them so simply bc their actions are bringing about important change, and finally, the introduction of the future dilemma White will have to face when he has to choose between the life his father has set out for him with the ministry and Black and Co's fight for justice for the common people hurt by the neglectful and corrupt authorities.