Inside a ternary ?: the expressions are evaluated - and \& { } constructs a code ref block which gets evaluated at runtime, to get at the name of the symbol table entry CODE slot from which a reference is taken.

This literally answers my question, and indeed I had realized myself after posting. Anyway I would consider this the "most side-effectish hack abuse one may have imagined for such a thing". This is certainly silly: one thing either has side effects or not, but... well to mangle the sybol table just to execute a block is... err... well... just as bad™ as I can imagine!