That is covered by the article, in the section “Em Dash and Spacing”. They conclusively say it depends on the style guide you follow and that what’s important i

That is covered by the article, in the section “Em Dash and Spacing”. They conclusively say it depends on the style guide you follow and that what’s important is that you’re consistent. Clearly the writers of the article follow the style of no spaces, because that’s what they used everywhere except on examples of other methods.