I found my mistake, but I would still like to get a couple things cleared up. Here is the fix:
<ion-content style="overflow-y: hidden;">
<h1>This stuff should not scroll.</h1>
<ion-scroll scrollY="true" style="width: 100%; height: 100%;">
<div *ngFor="let boy in boys">
<h3>This stuff should scroll.</h3>
This allows me to scroll through only the div at the bottom, exactly what I wanted. However, the height attribute for the ion-scroll confuses me. I thought 100% would allow all the content to be scrolled, but this is not the case - some content is still hidden and not displayed. I played around with ‘height’, and at about 60%, I am able to view all the content. However, at this point, I see a different amounts of the scrollable content displayed on different screen sizes. Can someone explain how the height attribute works for ion-scroll? And should this be something I define using vh? Thanks.