I think the idea of these math is to said that doing a 2D (x;y) mean is
better because we do not have this 360 modulo problem (x and y are
linears). Then you can make 2 means on each axis

then you can find the atan(Y/X) of this point (and this part is not
done in the given formula, you must adapt it this way).

I tryed with your example this gives almost zero (this is a modulo 360
answer always). Think about some IF exceptions because with the sign of
X and Y you must adapt the atan function (think about the X=0 dividing also)


tryed with you example It gives almost zero (4E-15) so it's ok