I don't think you're actually reading my responses. Messing with singing crystals is said to be illegal, but that's not even remotely what I'm talking about.
I believe the reason why it's brushed off is because there is precedence for it in the first place.
You yourself are missing the point that
@CountryMage is trying to make, though it would help if they had framed it better.
That point is that this is a known phenomena in the setting of the story. In fact, it is so well known that they have a law about it. That being that it is illegal to screw around with singing crystals because doing so tends to immediately invite other crystal lifeforms to the party to wreak bloody havoc on whoever happens to be there.
Thus, this means the psionic screams are known. The only real difference seems to be the source of the scream. Which, since it is already a known thing, is only being chalked up as, "Huh, so I guess it can happen that way, too." At which point it is simply noted and logged, and then everyone carries on with their day.
They don't even need to question Hiro about it. They saw what happened, and they saw the results of that happening.
Also, looking at it from the Doylist perspective, I can see this as something the author is setting up for a revelation that will come later on, and they want to be a little sneaky about it. Something that might feel like an ass-pull the second it comes out, up until Hiro or someone else goes, "OH! THAT THING THAT HAPPENED BEFORE!"