I always wondered this too - acknowledging that being issued a heading means not to compensate for wind, someone once told me "Runways don't have headings" [they have a QDM].
Based on that logic, I consider the instruction to mean "fly a heading that will have you track on the extended runway centreline". That balances out with the idea of an aircraft that is already airborne and tracking on the centreline.
If you've got a specific reference or some more sensible logic, I'm all ears!