I keep hearing DXA scans aren't that accurate either. @lizokryptonian on instagram has a few videos on it.

Yes, because DEXA does not directly measure tissues; it measures lean mass vs. fat mass. Lean mass is more than just muscle, so hydration changes affect the lean mass to fat mass ratio relative to total body weight. As a result, body fat % can vary, but you can control for it to some extent. It's useful and less invasive than other methods which offer higher accuracy.