From the docs:

Non-bracketing delimiters use the same character fore and aft, but the four sorts of brackets (round, angle, square, curly) will all nest, which means that q{foo{bar}baz} is the same as 'foo{bar}baz'

The code falls into this category because the parens are balanced. If you unbalanced the parentheses(sp?) then you would end up with a syntax error.