Is SmoothIntersections material function in Landmass correct?

Development Rendering
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1

I am looking into Water plugin, and I found SmoothIntersections function used in MeshBrush_Width material.

SmoothIntersection
SmoothIntersection2296×710 205 KB

This function can be written in HLSL like this:

void SmoothIntersections(float3 A, float3 B, float3 K, out float3 SmoothMax, out float3 SmoothMin)
{
	float3 diff = A - B;
	float3 t = saturate(0.5 + 0.5 * diff / K);
	SmoothMax = B + t * diff;
	SmoothMin = A - t * diff;
	float3 tt = t * (1 - t);
	SmoothMax += tt * K;
	SmoothMin -= tt * K;
}

This code is understandable except for the last 3 lines.
Why do we need the last 3 lines? In case where A == B (t == 0.5), SmoothMin will be less than A and B and SmoothMax will be greater than A and B. Is it intended?

I suspect that the function is supposed to be like this:

void SmoothIntersections(float3 A, float3 B, float3 K, out float3 SmoothMax, out float3 SmoothMin)
{
	float3 diff = A - B;
	float3 t = saturate(0.5 + 0.5 * diff / K);
	t = t * t * (3.0f - 2.0f * t);
	SmoothMax = B + t * diff;
	SmoothMin = A - t * diff;
}

MeshBrush_Width also have some weird nodes. I guess it tries to avoid some artifacts caused by the incorrect SmoothIntersections function.