Despite the fact that it's the same information? There's no distinction, in the example, between information that it's OK for Big Mouth to disclose and information that he can't disclose. Such forbidden information might exist and be known to Big Mouth, but Shylock didn't receive it. How can the only problem be that it was disclosed outside business hours?
If it happens in business hours then it's Conglomacorp's job to supervise Big Mouth properly and make sure he's not playing favourites (which as your sibling points out would be a Reg FD violation). If Shylock wants to trade on information then he needs to get it through the official channel where it's subject to compliance monitoring and all the rest of it. I'm fine with it being a crime for him to get information from Big Mouth in a way that bypasses those processes even if it turns out those processes wouldn't actually have blocked the information in this case.
