Front page template logic is horrendous legacy mess. While back I wrote a very thorough front page cheatsheet, I still can’t completely remember how it works.
You are right to notice that theme in your case doesn’t behave in same way as other themes typically do.
If you run down specific template being used (plugin like Query Monitor can help with this) it’s front-page.php, here it is in their github repo (and it seems to be moved in theme root, that’s what generator thing does).
It is very uncommon for this file to ship in a public theme because it will always override any other front page template.
In this specific case it is being used to implement that “business” configuration of the theme, displaying hero image and testimonials (look at its source). It chooses not to output page content for that case, that’s why it doesn’t appear.
So in a nutshell it is niche theme, built for a specific purpose, in a way that public themes typically aren’t.