Overall the advice is pretty bad and the article doesn't even follow its own advice. Instead we get this crap that doesn't care about accessibility and loads images with javascript (3rd party javascript!):

   <picture>
      <source ...>
      <img class="..."
           src="data:... (placeholder, no image)"
           data-sizes="..."
           data-srcset="..."
           data-lowsrc="..."
           alt="..."
           height="auto"
           width="100%">
   </picture>

Just don't use javascript for images and static content. It's better for SEO, for accessibility, it respects people's privacy, it works much faster.