He's an American, writing for an American audience, and thus he's using the units Americans use. There's absolutely nothing more scientific about one set of units or another (although different sets of units may be more convenient in different situations).

It prevents mistakes when we all use the same units and the SI are agreed by an international committee of scientists and engineers. It's one less thing to go wrong.

This isn't flight control software. It's a blog post. There aren't any "mistakes" to prevent. The website is not going to crash into Mars.

Good writers write for their audience. His audience is accustomed to thinking in miles.

It would be interesting to see the analytics - I'm not disagreeing and the site is presumably funded by American taxes, but people like the site aren't all American.

Great writers educate their audience.

Yea, but even in American high schools the metric system is taught for physics.

Inch / foot / yard / mile is a really small range compared to what metric can handle (anything), so in practice most science is done with metric units.

Wide ranges of values are handled exactly the same way in imperial units as in metric: multipliers. You write "0.00023 inches" or "5.48e4 miles", etc. It's just not as pretty.