Well, in this case the double is being passed to an external library (the renderer) right after this code, and the library expects a double.
Now, here comes a friendly rant: I have read the code style guide you linked to, but I'm actually not quite sure how to interpret it or what to think of it. To me it appears to be a mix of things that could potentially be important, and things that are just internal stylistic recommendations. And it makes no distinction between the two.
Take these three examples:
-"Always start a new line after the for statement."'
-"Do not write to global structures from a thread."
-"Do not use external libraries (e.g STL or BOOST) unless absolutely necessary".
The first one is clearly just a preference from MAXON (and I don't see why I should follow it if I prefer to structure my code in another way...). The second one seems to be a serious warning, and it sounds likely that violating this rule could cause a bug. For the third one, I have no idea. Maybe it is just a suggestion as well, and maybe linking my plugin with STL or BOOST could cause bugs. The docs do not say.
The recommendation for using MAXON datatypes also kind of falls into this category: I can't tell from the docs if it is just a style recommendation from MAXON, or something that could actually have an effect on my code.
To me, the code guide would be much more useful if it only listed things that are actual rules (or at least clearly separated rules and important advice from purely stylistic recommendations).