So, that U shaped pipe is supposed to be installed like an n instead of a u

That way; it has a big gap underneath that cannot fill with rocks (and sediment).

You put rocks underneath and rocks above and it becomes the french drain it was always meant to be!

As the water level rises above the bottom of the n shaped pipe, it flows into the pipe and hopefully down the hill toward the box drain.

It is clearly a bad french drain. (or an attempt at a DIY french drain).

An attempt where they forgot you are supposed to install the pipe upside down.

Seriously, if they just flipped the pipe it would probably work well enough.

The idea of the underside is to remain clear, so as water rises it can easily drain away down the kept-clear section of path.

In this instance, they put the pipe right-side up, and filled it with rocks (???)

Yes, most french drains use a full pipe with holes in the bottom - but the half-pipe should theoretically work well enough if installed correctly and in a manner that it doesn't flip upside down like this.