This is a Ternary operator.
It is essentially a shorter if statement.

Hi, can you elaborate on that test 17 ?

It is the only test I fail, and I don't understand how you would solve it using logic.

If you change your tests cases, a lot of solutions will invalidate, that's true.

But it's fine, that's what Beta status is for, so you can improve your kata :)

Please add a test case with input between 3.14 and π and specify whether isPi should return true or false.

Take 3.1405 for example.
I thought it should return false, but looking at the solutions it looks like everyone else thought it should return true.

So I think the kata description needs clarification on that point.

The filter callback function does not work like you think. It does not return a value, but returns a boolean which tells if the value should be kept or not in the filtered array.

The only advantage is less code as you said.
In most cases, using if/else is recommanded for readability.