An empty Array is falsey, yet an empty shaped Array is truthy
I will hazard a guess that Raku handles arrays in scalar context similarly to Perl 5: an array evaluated in scalar context produces the number of elements in the array. An empty array has zero elements, but a shaped array has a fixed number of elements. In boolean context, zero is false and any non-zero number is true.
Thus, an empty array (with zero elements) is a false value, but an array with a fixed non-zero number of elements is a true value.