Here is the node tree, I was following default cube, but his cheeses don't have these grids
My blend file is here:
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I think the underlying triangulation of the mesh being made visible is the result of an extreme 'Distance' value in the Bump node.
The Bump node has to make an approximation of slopes from heights, by, in some way, sampling heights of adjacent points in the map, and using the differences. It seems that if the differences are too great, and the slopes too steep, the approximation is not convincing, and exposes the underlying triangle normals, even though they are already interpolated by smooth-shading.
The illustration shows 'Distance' settings of: 1 (your setting), 0.5, 0.25, and 0.1. The last chunk shows your setting of 1, but with 1 level of Catmull-Clark Subdivision.
(The code, (at least the OSL version) points to this method of perturbing normals, given heights. What would make a really proper explanation of your artefact, rather than just a fix, would be a more serious mathematician coming along, and describing exactly why the approximation fails. If one comes along, please edit this answer!)