HTML has:

    <h1 class="c-post__title"><strong>How the inventor of the troll doll missed out on a fortune</strong></h1>

Nothing browser-specific about it.

I think parent is saying it rendered the strong tags as plain text

That's a weird behaviour to treat a tag as data rather than as a node. The HTML you provided shouldn't display "<strong>How the inventor[...]</strong>" but *How the inventor[...]*, should it ?

Yes. They’re not there until the page ships a separate set of CSS.

This must be some bug in whatever CMS they’re using to make it easy for writers to author webpages.