The part about <aside> is worded in a way that can be confusing. It implies that a <div> is always going to be displayed as a block, but an <aside> is some kind

The part about <aside> is worded in a way that can be confusing. It implies that a <div> is always going to be displayed as a block, but an <aside> is some kind of special element that could be either a block or inline. Whether it's "inline", "block", or "inline-block" is determined by the CSS for every visual HTML element. A <div> is not a block, nor an <a> an inline, those are just the defaults and can be easily overridden.