It's a general-audience essay, not one targeted towards the HN community. So unfortunately there's little opportunity to delve any deeper into what specific data structures are involved in holding the data and the difference that might make. There are data structures underneath in the excerpt you pulled out and they're so common in code that we don't even notice it. (Even something as simple as this: certain data structures are better for finding recent / first items and others are better for finding "top" / largest items. That has implications that ripple upward and can skew what users are shown.) It would be nice to consider the differences in how different data structures store data and their broader implications.