[BUG???] Correct way to calculate distance_to_gaussian_surface

[MrForExample]

In script: utils/ops.py#L153
Inside function distance_to_gaussian_surface(mean, svec, rotmat, query)
It calculates squared Mahalanobis distance by :
r2 = svec[..., 2] ** 2 * cos_theta**2 + d2**2 * sin_theta**2
But according to Mahalanobis distance formula it should be :
r2 = svec[..., 2] ** 2 * cos_theta**2 + d2 * sin_theta**2

Reference:
https://en.wikipedia.org/wiki/Mahalanobis_distance
https://math.stackexchange.com/questions/18776/mean-distance-between-a-fixed-point-and-a-gaussian-distributed-random-variable
http://www.open3d.org/docs/latest/tutorial/geometry/distance_queries.html

I have tested both formula, and both seem to work fine
Is this merely a trivial bug or is there any reason that I missed for your specific formula?
Please let me know :)