A Geography Lesson
There are people out there who just aren’t good at geography, and if you’re one of those people, it’s fine. But in that case, you probably shouldn’t try to call anyone out when they’re talking about it. Unfortunately, the person who responded to this post didn’t think that through and ended up putting themselves in the line of fire.
However, the original poster had no problem giving them a geology crash course. They even presented a visual aid! If that’s not a subtle way of calling someone out, what is?