Array creation method references are treated internally as references to a constructor of an array type. But this internal encoding doesn't make much sense to users, when it is leaked to them via an error message:

error: incompatible types: invalid constructor reference
  Runnable r2 = String[]::new;
                ^
    constructor Array in class Array cannot be applied to given types
      required: int
      found: no arguments
      reason: actual and formal argument lists differ in length

A more useful message would be something specialized like "array creation requires a single int parameter" or just "incompatible functional interface target type".