Section 3.11.3.1 states:

If the context item is an array, the UnaryLookup operator is equivalent to the following expression:

for $k in 1 to array:size(.)
return .($k)

This statement follows the conditional "If the KeySpecifier is not a wildcard ("*")", and I guess it is intended to be subject to that conditional, though this is ambiguous. In fact the equivalence holds only when the KeySpecifier is a wildcard; and is restated later in the section for that case.