This is a minor bug.
The hud.getResolution() function returns the resolution from the small GUI scale.
Would be nice to either get the resolution depending on GUI scale or get a hud.getGUIScale() function. (Or even have the GUI scale be a third variable to return from hud.getResolution()).

And in the case of getting the GUI scale I then mean a number, like 50% of the resolution.

Last option could also be to ignore the GUI scale and have it draw smaller anyways, but that wouldn't be a good solution imo.

You're correct, the method is supposed to return corresponding with the player's GUI scale.